It really depends. The 939 chips like the 3500+ and 3800+ have about 512kb of cache compared to the 754 chips like the 3200+, 3400+ and 3700+ which all have 1mb of cache. The extra cache can make a huge difference in future games that requires alot of power.
For games right now, the performance of a 3400/3700+ can be compared to the 3500/3800+, however. The 754 chips are half the cost of the 939 chips.
The advantage of the 754 chips are it's extra cache (which can make a noticeable gaming difference in power-hungry games like Doom 3) and it is also 50% cheaper while the 939 chips are more future proof (since there are boards built for them that also have PCI-E).
The Socket 939 4000+ just came out. It is similar to the FX-53, with 1mb of cache, but it's really expensive and you must be rich and/or spoiled to obtain such a beast.
Edit: Did i also mention the 939 chips are capable of running dual channel mainly because of the extra pins.