Team Fortress 2 definitely has the upper hand over Fortress Forever. You can tell by simply counting the number of servers running for each game: 3000 vs 40.
Coming from TFC, and before had my hands on TF2, I was a bit dubious about the changes Valve made to TF2, especially the lack of grenades in the game. Spamming with grenades is officially an annoying "newbie" thing to do in TFC, but we have all done that because it is FUN!
TF2 also changed the artistic style from a realistic environment to a "cartoonish" environment and caused more doubts to be casted over its success. (For crying out loud, people even complain when the gamma level is set too high in the upcoming Diablo III game).
But all my doubts disappeared as soon as I started playing TF2. There is really no need for grenades – just like the developers at Valve explained, without grenades, each player tends to focus more on what they are supposed to be doing with their specialized skills. The "cartoonish" style makes each class more lively, and gives each one a unique personality – the muffed calls from pyros, the weird affection between the heavy and his gun, the somewhat vulgar but definitely hallarious taunt from the demo – all added special touches to the already addictive game play.
Fortress Forever, on the other hand, lacks all this. My first impression of FF was that "wow this game is soooo frigging quiet!" You can run for miles in FF without hearing anything. zzzzz… … … The character animation definitely needs more work – the movement of the models looks too robotic. The worst and most annoying part is the mechanical voice of the announcer. BLUE. TEAM. CAPTURED. FLAG. YOUR. FLAG. IS. STOLEN. Automated customer service phone systems don’t even do this anymore, why would FF go this route?
FF boasts a "realistic" environment as one of its selling point, but I find everything rather "artificial", far from being "realistic". TF2 on the other hand, looks more realistic with barnyards and train yards.
Therefore, TF2 is definitely superior as of now.