I'm not cross-compiling much, but I've used Linaro because it's trivial to install and "just works" - in my case, for
experimenting with u-boot (I wrote that for 10.04, but it continues to work after the upgrade to 12.04).
I guess others (twobob, knc1, NiLuJe...) will be more knowledgeable than I am, so you may want to wait for their opinion