Yhe graphics plug-in from nullDC are slower but it seems to be more accurate for most games (sonic adventure 2), and slightly less accurate for others (street fighter 3).
While Chankasts graphics plugins are indeed faster... I also think it doesnt have a frame limiter. Of the four games I have tested using only nullPVR the games would bounce between 58 and 60 FPS at times but never above 60. Overall I recommend the default graphics plugin. ~35+ FPS and better accuracy (almost looks like it's on the real thing) makes for better play in my opinion.
Edit: On second thought the Sega Swirl was flying at 120+ FPS this morning when I tried to run Sega V rally... But in game I could never get above 60.3 FPS.. May just be a coincidence. Someone will have to ask Drk on IRC I guess.