The Matrox G400 was neck-to-neck in performance with proper TNT2s and Voodoo3s, but had poor quality drivers at launch (no OpenGL support). After the drivers matured, you're left looking at a clear winner in terms of features and image quality. Most of the time in performance as well. Last time Matrox had a real entrant in the race.
TNT2 and TNT2 Ultra had the muscle, but depending on manufacturer the analog display quality could be ok to bad. Also had to be careful about picking the drivers. On Windows 9x, I remember Detonator 3.6x gave the best performance, especially in 32-bit. 5.xx series also had some good drivers. After that, the scores and performance seemed to generally decrease as the unified driver was optimized for the Geforce lineup.
Voodoo3 had great analog quality (desktop/2D), but lacked in certain features such as 3D rendering in 32-bit color. Unless you had a top of the line rig, you wouldn't care for that tho. People wanted high frame rates and to get those most of use needed to drop to 16-bit color anyway. Voodoo3 also had Glide, which neither TNT2 or the G400 or G400MAX could give us... and the drivers aren't as fickle as the nVidia Detonators.
Not sure if a sub 1 GHz P2/3 system really benefits from having GeForce and newer class video card as the games that could use those generally required more oomph on the CPU-side as well.