I just completed fallout 2 and Im looking to start my next game, should I go with tactics or fallout 1? Why?

Probably the first Fallout. It will be much easier to go from Fallout 2 and straight to the first one considering they basically play the same, only Fallout 2 has tons more content and improvements made from the first game.

Tactics plays quite differently from FO1 and FO2, as it's not necessarily the RPG that the first two are and has a much larger emphasis on tactical combat. Best to finish off what you already know with the first two games, and then jump into the much different experience that is Tactics.

Fallout and then Tactics.

Pretty much for the same reasons as Legion64 stated.