I personally would not recommend to use the largest pool of all, because btcguild is quite close to 51% hashing power of the whole network. If someone reaches more than 51% hashing power of the network than he is able to split the network in two branches and the do several evil things.  If interested read more here  http://thegenesisblock.com/the-51-attack-what-bitcoin-can-learn-from-alt-coin-experiments/

I'm not saying btcguild would ever do that, I just want to point out that it is not necessary to give them the opportunity by adding my miners to their pool.

And: As everywhere else in real life you should not feed the rich....