64 Bit all the way.

Processing power
Ram Recognition
Board Architecture
North Bridge 64 Bit > 32 Bit

The only thing I can say negative up till now about 64 Bit is that early adopters kinda got screwed with support for those systems. That is not true so much anymore. Secondly, I personally am a big proponent of "clean" and "constant" power coming in off the rails of the power supply. This is more important in a 64 Bit machine over a 32 Bit machine. A marginal power supply is not a deal breaker, but like I said me personally, am willing to spend up to get the more robust configuration.

Don't make me have'ta Troll ya Bro!