The reason I would like to go for and AMD based system is because of their much better CPU scaling support. My old system, which I built in 2004 had good CPU scaling and could quickly switch between 3 clock speeds, the lowest of which was slow enough that the thermal output from the CPU was very low, so that my system ran cool and Quiet. More recent AMD CPU improve on that by allowing different cores to run at different speeds in order to better match the clock speed to the workload.
In contrast my Current Intel Core2Duo based system (see the 'My System' Link), only has two CPU frequencies, the slowest of which is 1600MHz, which is to fast and hot for background idling, and if any thread on the system maxes the CPU core it is on, the whole CPU has to switch to 2400MHz, wasting even more power.