You posted almost EXACTLY the same question I've been running through my mind the last few days, except I've been looking at the MSI S939 board.
DFI LanParty UT nF3 250Gb
Pro
More mature platform
More features than you can shake a stick at
Low return rate
Con
S754 platform - limited future upgradeability
MSI K8N Neo2 Platinum
Pro
S939 platform - newest processors, run cooler, less voltage
Approximately the same price as S754
More features than you can shake a stick at
Con
First-gen NF3 for S939 - buggy
Higher return rate than most S754
BH-5 memory problems
Antec power supply problems
As I plan on using both my Antec TruePower 550 and my 2x512 Mushkin 3500 lvl2 BH-5, I have a double-whammy chance of running into problems with the MSI. But I don't want to buy into the aging 754 if at all possible. Although, by the time I decide to upgrade again, I'll most likely be buying an SLI board anyhow.
As far as waiting for NF4 SLI boards, again you run the risk of opening the "first generation bugs" can of worms. Plus their $200+ pricetag is really putting me off. And the fact I'd need to purchase a PCI-E video card on top of the motherboard/CPU combo.
So I guess I'm kinda leaning towards the DFI, myself. In most cases it doesn't make a lot of sense to buy previous generation equipment if newer can be had for the same price, but in my case it's sort of a toss-up.
As far as your case, I've seen many good reviews of the DFI board and nearly everybody who has one seems happy with it. So I'd say go with the DFI.