What GCSmith said. Wait for the Codex to come out; make comments then. Almost anything thrown out there now is speculation - some of it much wilder than other.
How about Tau with guard allies?
I'm a staunch and hardcore proponent of the greater good... I love me Tau. I'd wait for the new dex to see if the Tau'Va is on its ***. I know we're getting some boss new robots and drones (maybe some new rifles and shooting rules) but otherwise it's probably going to be less broken than before, but all the super glue in the eye of terror couldn't fix the Tau without making them on a par with the IG PLUS giving them an edge (or even just a decent WS and some power weapons).
Good Tactical acumen + Bad Dice Rolls = Chronic Systems Failure / Turn 3 concession
It's 2 or 3 edition since I've played either, but I started playing 40k because of tau in 01 and I've always toyed with idea of fight for the greater good again. The models are just so freaking awesome, so freak awesome...
IG is a hammering gun line where as tau are ranged hunters. They will require more finesse but the way you can load out crisis suits and other tech savvy units to support each other is worth the tactical work.
If you for tau, it will require more risks but also more flexibility, especially more so with all their new goodies.
P.S. join the farsight enclave, it's the bees knees.