In this post I am going through my choices and explaining why they are ranked where they are.
Mech IG has absolutely ludicrous fire power. It can blast half of an enemy army off the board on turn 1. Additionally, it has all the small things that can really help in some games. Part of this is from allied DH inquisitors which will no longer be available a few months from now. There is also the reserve manipulation abilities of the army which make reserving your entire army against an alpha-strike a very risky manouvre. On top of all that, IG has the ability to field rediculous amounts of AV12 vehicles, making it one of the most resilient armies because it can take losses and still deal out the pain.
Space Wolves and Blood Angels
I haven't done enough playtesting yet with the Blood Angels to really know if they are better than Space Wolves. I am planning on doing a comparison between these two excellent codices in a later post. Both armies combine speed, shooting and assault into their game. From the lists I've seen on the interwebz, BA tend to be faster while SW are usually shootier.
I may have ranked these guys too high because they are a bit of a one-trick pony. With everyone gearing up to kill the AV12 spam of IG, Eldar mech got caught in the crosshairs. However, mech Eldar still excels at objective games because of their speed and the durability of DAVU Holo-Falcons. They are also a hard counter to assault-based armies because they have the speed to zoom away from most deathstar units. Foot Eldar is similar to Tau: good at killing but awful at moving out and holding objectives.
Orks have, in my opinion, the most durable troops in the game. They can pack more T4 wounds into an army than anyone else. They basically have two very strong builds: Battlewagon and Foot. I used to play Battlewagons but I sold that army because I didn't like the style of play, and now I'm working on my Foot army. Trukks are easy Kill Points and don't carry enough Boyz to be effective, while bikers are overcosted. Ghazghkull is a beast in CC. People will argue that he is only effective for the one turn where he Waaaghs but my response is that he only needs one turn. Anything else he kills during the game is just gravy.
The Vanilla Marine codex has only a couple advantages over the Wolves and Vampires. First off is Null Zone, which is IMO the best of any Chapter's psychic powers. Then they have combat tactics which is an underrated but extremely useful special rule in the hands of a good player. Combat tactics is what makes foot marines an actually decent army. Not amazing but it can still compete. There are also a couple little things like the Ironclad and thunderfire which are not available to the other codices.
Chaos Space Marines
Like it or not, Lash of Submission is still an excellent psychic power. I'd say it's still the best psychic power in the game. Combine it with Oblits, one of the best (if not the best) long-range unit in the game, and Chaos are a great shooting army with decent CC punch. We all know the list; not much else to say here.
Ahh, witch hunters. There are two ways to play them: shooty with 3 exorcists and inducted guard, or Immo/rhino rush. Then you can also do a hybrid army involving exorcists and sisters with rhinos. All are decent builds but all have their weaknesses.
DE epitomize the term "glass hammer". They can give a punch but can't take one. The only way for them to survive is to fill up the FOC with 12 vehicles. Lately we have seen Dashofpepper do very well with Dark Eldar, showing that they can still compete with those brand new 3rd and 4th edition codices.
I've never played Nids and never will, but I feel sorry for the die-hard Tyranid fans. They still only have one viable build (Nidzilla), and it got slightly better than the old codex. It retains its classic weakness, lack of long-range anti-tank. Hive Guard are the one exception which means everyone is taking them. So now we are back to where we started with every Nid player running the exact same thing.
Daemons are the best close-combat army in the game, with a variety of tough units. They also have decent support fire to pop tanks for the CC-beast to eat the guys inside. So why am I ranking them so low? You've probably guessed, Daemonic Assault. To be honest it cripples them too badly. Deep striking is a fairly easy tactic to defeat if you have good bubblewrap units, and any shooty army should have them. Others, like Eldar, can just fly away because they're too fast for most Daemons to catch them.
Ahh, the good old Black Templars. The codex is still held afloat by their Furious Charging, Prefered Enemy assault terminators and their ability to spam land raider crusaders. If you can handle the LRCs, you win. If you can't, you lose.
With DH you pretty much have to go down the route of LRC-spam. Sometimes an IG platoon is included for bubblewrap and additional firepower. The classic smoke launchers (weapons can only glance) are a nice bonus and DH get a better crusader for 258 points than marines get for 275.
The Crons are still kept alive by 3 units, The Deceiver, Monoliths and Scarabs. Those three units are fantastic, while the rest of the codex is pretty much crap. The Crons have some glaring weaknesses in the tournament metagame. Among other things, they cannot deal with lash+oblit chaos or seer coucils.
I like the Tau a lot but they really got screwed by 5th edition. While they can pump out a lot of firepower, it isn't enough to beat the really shooty armies like IG, CSM and Eldar. It's also very easy to pin them down in a corner, because they have no counter-charge units (kroot are too weak) and no real way to move out and capture objectives. The whole army suffers from morale problems so you'll often see vast amounts of units run off the board after taking a few casualties. BS3 is a big problem, along with lack of psychic defense. They need a new codex badly.
Dark Angels are like codex space marines, minus everything fun and interesting. Their assault termies suck, they have crappy psychic powers, no chapter tactics and everything is 10% more expensive. Their only good unit is the AV14 land speeder. While awesome, it doesn't compensate for the rest of the codex. Their bikers can get a first turn charge but for 40-50 points per model it isn't worth it.
Part II will answer the comments and explain why I don't like the tier system and a couple other details.