The only other 3d console at the time was the ps1, which had HORRIBLE graphics. Unfortunately the ps1 still out-sold it because it had FMV (ooo video, that really adds to a crappy game!) and the games were about 10-15 bucks cheaper. The ONLY limitation of the n64 at the time was texture size, not because of the hardware (which could handle about anything at ntsc resolution) but the cart format.
Bar, none, without question, the n64 had the best graphics at the time. Don't believe me? Pick any n64 game, look at the year, and then pick a similar ps1 game from that year. It'll look horrible in comparison (although it might have more levels or some fancy videos). Oh and remember that emulators can add fancy blending filters to the 3d on the ps1, so turn those off.