I prefer a reboot of TFC[0].

I wish FF[1] had fared better, but it was too late, especially with TF2 coming as an official title.

There is TF2C[2], but I have yet to try that one. Interestingly, it's still going strong with relatively recent content updates[3]. I'll give it a try, but at first pass, the gameplay appears to deviate too far towards TF2 and away from TFC.

     0: https://en.wikipedia.org/wiki/Team_Fortress_Classic
     1: https://en.wikipedia.org/wiki/Fortress_Forever
     2: https://en.wikipedia.org/wiki/Team_Fortress_2_Classic
     3: https://tf2classic.com/