Nothing tops the lightning in a bottle of T1. The game was being re-invented every week and it's impossible to capture that kind of magic intentionally.
Having said that, T2 with classic is probably the best as it has the most complete and refined experience. You can have everything from minimal, no gen or turret bases to massive bases with vehicles. How the game plays can radically change based on what's in the map and how it's designed. T2 also has the best inventory system of any Tribes game.
T:V, T:A and T3 have all been increasingly smaller games with more and more features removed.
T2 even has little things, like tournament mode that makes the teams Storm and Inferno and locks players to one team and won't start until an admin forces the match to begin. When it first came out, it had a clan system that let you join a Tribe and have your username appended or pre-appended with your clan tag. It had built in email and IRC.
It's absolutely insane how many features T2 had that were completely dropped in all future iterations.
