Sisters of Battle.
All I can say about this army list is that it desperately needs a proper codex and not a white dwarf article. At the moment it is woefully lacking in everything. They don't have enough options for vehicles, no flyers and not enough options for their infantry choices. Under 6th they should probably be put away until GW give them a proper book.
The Space Marines have gained something this time around! Yay! Moving and firing a heavy weapon, being able to overwatch and the host of new psychic disciples have bumped up their playability now. Their tanks are more survivable under the hull point system though you do have to adapt your thoughts to rhinos and realise that they are there to get you half way up the table now. If they survive then yay. Obviously this applies to the other space marine codex as well but I included it here because it is a boost for this codex. Since 6th I have had much more luck and won more games than I ever did under 5th. The changes have been good for them. Tactical squads still need close combat weapons or the option to take them though.
This army was a nightmare under 5th and have got worse under 6th. Although the new edition has made the right move and favours shooting over combat, Space Wolves are still IMO the best close combat army in the game. It's for this reason that they are the commonest ally I see taken by other players.
They get so many options for weapon load outs that they can almost cherry pick like Eldar do. Their rune priests can deny the witch in an area on a 4+ which is just crazy. Long Fangs can split fire with heavy weapons which is a huge bonus.
I think 6th edition has done this codex very well.
Under 5th the Tau army has always been a one trick pony - they sit back and shoot with scary accuracy. Close combat screwed them severly and that was an opponents saving grace. 6th edition has changed that. The codex still desperately needs an update but can now hold it's own a lot more. Overwatch has helped stem the assault problems and they can pick vehicles apart a lot better. Much like with Space Wolves, I fully expect the Tau to end up relegated to the ally detachment until they get a new book.
Under 5th the Tyranids were yet another nightmare to deal with. They don't have good shooting so they became crazy good at close combat, as you would expect. However I feel that they were made too good. The current codex did a nice job of toning them down and bringing them to an equal level with everyone else. The problem, once again, is that some units have become obsolete. Genestealers won't see use under 6th and why take carnifexes when trygons are a better option?
Overwatch has been a balancing factor for other armies but if you get into close combat with tyranids you can just count your unit as a speed bump.
Tyranids are still a really tough army to play against and have come through 6th edition in a good way. As with many codexes, it will just take players time to work out what does and doesn't work any more. Like the hive, they'll have to adapt.