Quake 3 Weapons Factory Arena mod was my jam. 16 vs 16 on dial up in ~2000-2002 was amazing. Tribes was also fun, as was UT2k3 with low grav. I always liked ridiculous mods. TF2 was / is also great, especially the madness that was 3-pg: https://m.youtube.com/watch?v=egGAPrNCj0M and the Wacky Races maps: https://m.youtube.com/watch?v=oPP7PnEtTmQ