Between New Vegas and 3? New Vegas blows 3 out of the water, if only for the reason that I had nothing but contempt for the whole "dearest daddy is the most important man in my little world" story arc you were shoe-horned in to in Fallout 3.
I recall when Extra Credits used to be on the Escapist, and they attempted to suggest that New Vegas lacked the player-character definition which existed in 3, and that was somehow a failing in New Vegas. All I could think during that video was "They must never have played the original Fallout games." Tabula Rasa characters are much more compelling in a sandbox-world environment. _I_ want to define _my_ characters' motivations. I didn't leave Vault 101 to "find daddy." I left because A) They wanted to kill me, B) There was a great big, wonderful wasteland to explore! When I accidentally stumbled upon Liam in the virtual reality Vault, I wanted to just leave him there to rot and continue on my merry way. But no. All the dialogue options when you find the daft bastard are variations of "I missed you, papa."
And, to a lesser extent, when you "first" meet the Brotherhood of Steel on your way to Galaxy News Radio (or, in my case, when I was already level 30 and just happened to stumble across them while enjoying myself exploring), I would have much rather a dialogue option of "HA! You kids just sit tight for two minutes, and watch how a professional deals with Super Mutants." Not exactly the same as my complaint about the daddy-issues forced upon your character, but it still would have been nice to just shut down that high-and-mighty [lady] by demonstrating to her that brute force is not the way to wipe out FEV-muties. Honestly, they would have suffered zero casualties if they just let me move in ahead of them.
New Vegas, on the other hand, handles the matter of self-control and roleplaying much more appropriately. New Vegas doesn't force you to have specific feelings for Benny; they let YOU decide how you feel about the man who put a bullet in your head. That's the right design choice to make for a game in the Fallout series. You can try to haggle with Benny. You can try to kill him. You can torture him. You can _ignore_ him. THAT is what makes for a great Fallout game! Freedom of choice. Having so many different end-games available in New Vegas, even if they all used the same general setting, means I'm the master of my own fate. As it should be. Other factions may have attempted to use me to their advantage, but ultimately I decide who wins; not a pre-scripted tour of seaside DC following a robot I would have much rather attacked and destroyed, rather than sit around and watch it give hugs to lightning rods (fuggin' Jingoistic monstrosity . . . ).
The only major complaint I had in New Vegas was they wrote themselves in to a corner and HAD to make the game unplayable after Hoover Dam. The number of variables and dialogue trees to program in after that point would be equivalent to two or three more entire games. That was frustrating, because I really wanted to SEE the aftermath, not just be told about it in a slide-show. But at least I felt like I had some true agency up until before that point of no return.
Regardless, I still consider Fallout 3 far superior to most other games released in the past 10 years. It's not perfect (nor is New Vegas), but it felt like a step in the right direction amidst a continuing trend leading away from good games and respectful design decisions.
Out of all five (because we do not talk about . . . /that/ "Fallout" game), I still have a special place in my heart for Tactics simply because it was the game which really got me in to the Fallout universe (despite the canonical issues, which wouldn't actually be issues with a halfway decent writer to patch things up . . . ). Between 1 and 2, despite the clock ticking down to doomsday, I felt the original Fallout was actually more accessible and playable, and ergo enjoyable. After all, I didn't NEED to build a combat-capable character in Fallout 1 to beat the bloody tutorial temple like I did in 2 . . .
However, I can't really choose a clear winner between the isometric games and the 3D games. They're too different and too distant in their respective eras.
I hope Fallout 4 finally bridges the gap between Tactics and the other canons. I want someone to clue in and realize the fuzzy Deathclaws don't have to be an evolutionary offshoot of the reptilian Deathclaws (which makes NO SENSE), and instead are just simply /called/ Deathclaws because it's not exactly a super unique name. Or that a splinter faction of the Brotherhood of Steel essentially abandoned its ?sacred? ideals and started to unite humanity with its evolutionarily-redirected cousins (imagine the potential there for twisting that in to something sinister and compelling, as a ?Universal Brotherhood? faction, a la Shadowrun lore). That the robots and the Vault 0 storyline needn't be ignored entirely, but instead suggest that Vault 0 was a P.R. manoeuvre by VaultTec to lull their primary financial backers in to believing they would have a safe place to wait out the apocalypse. Yes, there were some definite visual design and aesthetic problems with Tactics when compared to the Retro-Ditry stylization that made Fallout special, but of all the elements of Tactics to gloss over and pretend didn't exist . . . why not that one?