Really does depend what you want to achieve - if you want excellent results in gaming - you need to push your GFX card - so water (and ideally a TEC) is the way forward. If you love tinkering and having the fastest darn machine around, then phase is for you. It's fun and rewarding, and well worth the investment in time and effort (and not that expensive, you can pick up a decent Mach 2 GT for around £200 these days which is brilliant)
If you can't afford to lose anything, or really need stability...
(Or you can go the whole hog, Phase on the CPU, Pelt on the Gpu and cool it with a chiller - was great fun to set up and gave great results!) - but check my sig - each to their own! I must be getting old, 'cause I just want at least one machine stable.