Nforce 2 hands down.
Name one other chipset that had that many features.
It had a fully capable APU that rivaled anything that creative could throw out there. It remains one of the only solutions ever do be able to decode a Dolby Digital 5.1 stream in real time.
The video was the best in the business. While it didn't support DX9, there was nothing that even approached the level of that video.
The memory controller was the best in the business. With dual channel and the ability to OC to unreal levels there was nothing not to like.
440BX was a classic, no doubt. But i dont see how it revolutionized the intel chipsets afterwards. Intel chipsets were always good, 440BX was just another addition to an already successful line of products. Nforce 1/2 was simply a revolution for AMD, and it marked Nvidia extremely successful entrance to the chipset market. (I kind of wish we were back in the days of the Nforce 2 and the AXP and the P4. Hell i still remember my 486SX, and then my Socket 7 Cyrix 150+)
-Kevin