I haven't played 2 or Tactics of yet. Started on 2, but I feel like it's running into the same issue that I had with F: NV, wherein the things I want and expect from a Fallout game are pushed aside for subversions of such. Greater number and lucrativity of towns, an intense story focus which drowns out some of the mystique of the Wasteland, and just a generally less exciting atmosphere. I'll make my judgement when I finish it, but that's just the same relation I had of F3 to F:NV.
I will not deny that Fallout 1 is the more focused and innovative game, and contains elements I think lack in the 3D ones. However, Fallout 3 gave me an entirely new experience when I first played it. Maybe it was the order I palyed them in, but Fallout 3 was simply more impactful. I've seen people sort of malign the exaggeration of qualities that Fallout 3 had (while also claiming it wasn't wacky enough(?)) yet that iconography made it reach far beyond regular gaming culture. Perhaps I'm just a sucker for the iconic. Those gaming moments I remember the most though are usually big factors in me putting them up on the wrung. Exiting Vault 101, the return of the Enclave, and moments of being lost in the Wasteland were far more impactful to me than leaving Vault 13 or finding the Water Chip.
Fallout: New Vegas is in a lot of ways a better game than Fallout 3, particularly in its interesting use of game mechanics. Obsidian was given a lot of time to figure out the limits of what they were working with and use them expertly. One particular mission with a radiated Vault was a great highlight for me. But battling for control over a near fully refurbished city and quests which cover the same (FAR less interesting) ground repeatedly, I feel like the Wasteland wonder was completely ripped from the game. It became more like Oblivion than Fallout. I didn't happen upon settlements with surprise, it became mundane. New Vegas has a lot of minor annoyances, like some areas being far too big for what they contain, many choices but no really clear way to get to any given choice, and a revision to some of the gamepaly elements which I jsut don't agree with. That's secondary though when we're talkign about a series as a whole.
So for me:
1. Fallout 3
2. Fallout
3. Fallout: New Vegas