This is from a letter I sent the guys at Bell of Lost Souls in response to their best army ranking thing. I originally posted some of this in the comments on their site, but here's the EXPANDED EDITION complete with info about me!

I play in Charlotte, NC. (I've also been in Sarasota, FL, and Athens, OH since the new edition).
We can get (at the FLGS near my place) upwards of 20 players in for tourneys. There are a few of us who play very frequently, and the others show up when they like. I know also that there are 2 other stores in or close to our city, both of which have thriving groups of gamers. Most all of our players around here have 3-4 or more armies. A very select few (myself included) have enough armies that we're embarassed to give a number (mine is: 10 40k armies, 6 fully painted. 4 fantasy armies, 1 fully painted).
Our tournament scene is pretty decent around here. We have more than our fair share of strong players. For instance, my Orks took 2nd in our local 'Ard Boyz and then 5th in the second round. Sadly, we don't have a large number of tournaments. But, the quality makes up for it.
I've probably played 150+ games of 5th edition, since it dropped.

Here are my top picks for the best 40k armies.
I'll just expand on the list I've already put up.

1. Space Wolves
-Unequivocally brutal. Multiple close combat charges = lots of dead things. Loads of HQs (most games I've played are 2k on up). Benefit from the new Marine book in a lot of ways.
Here's a list I faced in 'Ard Boyz round 2 that really shows where the Wolves still shine. 3 Blood Claw packs in Land Raider Crusaders. 2 small Grey Hunter packs with Wolf Guard leaders in Terminator armor with Assault Cannons, crouching in cover. 1 Venerable Dreadnought. 1 group of Wolf Scouts.
Basically, wolves have all of the ranged punch of other Marines, but they get an extra boost in CC. A single squad of Blood Claws can tear through enemy squads 2 at a time or stop a Ork Charge dead in its tracks. Fully kitted Wolf Guard squads can go toe to toe with Nob Bikerz and come out on top. They have all of the advantages of Orks, except they take quality over quantity. Bizarrely, this tends to work very well for them.

2. Orks
-We don't see the nob bikerz here (one guy is working on a whole biker army, but not even remotely the same). Horde is the style of the day, slightly mechanized horde is also popular.
Orks have the best troops choices in the game, and everyone I've seen play wants to capitalize on it. Large groups with sluggas and choppas or shootas have killing power and staying power. KFF Big Meks or Battlewagons help them get to the line generally unscathed. Additionally, a Warboss and a unit of nobz coming out of a battlewagon or trukk can lay some serious hurting down, even without their bikes. Orks would have spot #1, but Wolves will beat them at their own game.

3. Sisters
-This is all due to me, apparently. I'm the only one around here who plays them, and I've got a reputation, I guess.
Rending bolters and 3+ invulnerable saves when you need 'em. A highly faithed mechanized Sisters army is the bane of bugs and orkz as well as Marines. Flamers and Heavy Flamers all over the place (especially the Immolator- 12" move and fire twin-linked Heavy Flamers? Yes, please) are great for hordes, as are the cheap BS4 bolters. Add in the ability to make all of our weapons rounds rending for a win against Marines. Average combat abilities would drop us down, but we also have 3+ invulnerable saves on demand in our Stubborn LD9 units.

4. Blood Angels
-Dante. Lemartes. There are a couple of really good BA players around here who drop the army occasionally.
Basically, Blood Angels are like the poor shadow of Wolves. Quality assault troops, but not near as many special close combat weapons. Dante's re-rolls and dropping everyone else's BS and WS make him a necessity for the middle of your front lines. Dante and Assault Vets plus Lemartes and the Death Company supported by a couple of regular squads will punch through any line you care to show me.

5. Black Templars
-Preferred enemy, need I say more?
Preferred enemy in assault with lots of power armored guys. Shooty squads with a few guys and neophytes for ablative wounds. Add in a couple of Land Raiders, the Emperor's Champion and maybe a Marshall. Blam, yet another assaulty Marine army like the Wolves, yet still not as good.


6. Imperial Guard
-Russes, hellhounds and lots of heavy weapons. Even the relative new players can drop an opponent rather handily. Oh, don't we all dread that new codex ;)
Think of 3 stripped down Russes, 3 Hellhounds and then as many guys with grenade launchers, missile launchers and mortars as you can toss in. Bring a few lascannons and heavy bolters for luck. Drop one squad in a chimera to make a dash for any far objectives. This army is template city. Anyone who thinks cheaper Guard and more durable Russes aren't going to propell it to the top slot need to step back and take a good hard look at their biases. Guard currently have a resiliant pie plate dropping tank and loads of men around it to drop small templates and just shoot the enemy to hell. A good guard player (with some really great luck) can drop my army in 3 or 4 turns without taking significant losses.


7. Dark Eldar
-My buddy is the only one who plays these around here, but he is rightly feared (except perhaps, by his dice, which always roll 1's on the vehicle damage tables). WWP kabal with lots of agonizers and dark lance shots.
Archon with Incubi, one of the most lethal close combat units in the game. Add wyches to tie up termies or other elite assault troops. Warriors mop up the rest of the army with decent shooting and close combat punch. Dark Lances on every Raider means vehicles get to do nothing all game. Dissintegrators on Ravagers means that Termies or regular marines will be dropping. Superior mobility means they hit the enemy where they want, when they want. Horrorfexes and the like mean that anything that can be pinned that needs to be pinned will be pinned. They only suffer against horde armies.

8. Chaos Marines
-They probably should have been higher, but we haven't seen them a whole lot, lately. Plague Marines are a problem everywhere.
Nobody here takes a Lash. Not too sure why, but even with that, Chaos is not as much of a threat as some of the other big nasties. They have relatively good staying power, but they seem to (as played here) lack that killing punch that wins so many games. We have a couple of dedicated Chaos players who are cutting their teeth on somenew Marine armies, so the Warp Gods have been strangely absent as of late.

Honorable mentions:
Vanilla Marines (and Dark Angels)- Just too mediocre unless you spam special characters, even then, they're not a super powerhouse. We have loads of people playing new Marine armies right now, and the Special Character based ones shine and come together as a whole. They usually just still are pummelled by any of the top contenders, however.
Eldar- We just don't see them often. But when we do... There can be all hell breaking loose. The specificity of their Aspect Warriors lets them compete in any game phase, while Guardians and the like provide more than adequate support.
Nids- They can't out horde orks, so many player are frustrated with that. The rise of mechanized armies of every stripe has also taken its toll. If they can't open up transports to eat the men inside, they're kind of stuck sitting there until the heavy weapons from the top hatch of the transports blow away the big guys. Still, in my book, a good army. Players are just having trouble adapting to 5th here. Still, a nice change from seeing them be the "We own everything" army they were in 4th ed.
Tau- Really we have 2 Tau players here. Both have good armies that can do a hell of a lot of damage. S5 basic weapon? (Thought your transports were safe from small arms? Think again.) Railgun submunitions which don't just disappear? However, JSJ has been hampered by the new cover system.
Daemons- Seems like everyone has a daemons army they're working on. Still, however, the randomness and dangers of deepstrike have hobbled them in many games. Maybe as people get more familiar with them.

Not so honorable mentions:
Necrons- Huge nerf to their ability to take down tanks coupled with more tanks showing up = sad, sad necrons. Not necessarily bad, as they needed a small toning down, but they need a bit of fixing still. The Monolith is still ridiculously hard.
Grey Knights- No one plays actual Deamon Hunters. Everyone plays Grey Knights. Grey Knights would be great, if you could get more than 10 or so in a 1500 pt list. I know it's an exaggeration, but the basic criticism is correct. There are too few of them.