Yes, dual channel memory is a plus for the skt939 processors.
but if ur not overclocking then a skt754 3000+ is clocked 200mhz faster than the skt939 version, and while not having dual channel memory is still quite a bit faster. I went skt754 because i probably wont be overclocking (i like warrenties). My 3400+ is faster than the $50 more expensive 3500+ in most tests, but i wont have as high of an overclock (possibly) and not have as good of a possiblity for upgrades.
The skt754 3000+ and 3200+ overclock quite well however, and the new 3400+'s are supposed to get up to around 2.7-2.9 on an overclock.
Either socket is a good choice in my opinion, but it depends on what you want to do with your computer.