I've only played Fallout 1 and Fallout New Vegas to completion and about 40 hours of Fallout 4. Of those, I really have to say that I liked FNV the best. I know it's stereotypical and I wish I had something more unique to say, but yeah lol

New Vegas and 2 are the obvious choices, but I'm going to go out on a limb and say that 76 is third. Speaking as someone who didn't enjoy 3 and 4, 76 fixes a lot of my gripes with those two games while simultaneously having some of the most creative world building in the series. The game taking place shortly after the bombs dropped makes Bethesda's heavy focus on pre war America fit a lot nicer than everyone constantly talking about a war that happened 2 centuries ago in 3 and 4. The various factions, from the Responders to Foundation to the Cult of the Mothman, are creative and have a lot more depth than any faction or settlement in 3 or 4, and feel a lot more interconnected in the world. Appalachia is also just really awesome to explore

New Vegas and 1 are the best. It's kind of the obvious take but that's because it's true.

Fallout 4 is my favorite followed by New Vegas. The gunplay and relative ease of moddability has me at over 1,600 hours in-game, despite all its issues, the less-than-impressive story, and the like. NV somehow feels a little sparse in comparison to even FO3, but the storyline and dialogue more than make up for it. Plus wild wasteland, of course, which should be in EVERY Fallout game imo.

Fallout 2 is the best. I've played through many different ways over the years.

For some reason 4 is cripplingly addictive for me every time I pick it up but I can't get into any of the others

I would probably agree. Still has a pretty active modding community which is nice.

Fallout 3 has a nostalgic place in my heart and Fallout 4's new mechanics and settlement building were a fair amount of fun though

I really like the first game. Talking the master out of their plan is incredible and the game world is so interesting to discover. I learned a lot of new English words from it, and because the characters talk with slow text on the screen it is easy to follow compared with speech.

honestly probably fo4, though its a close match with fo3

the gameplay improvements and loop just entertains me for significantly longer, despite fallout 3 having better atmosphere, and fallout 4 having a lot of issues in practically every part of its design

at least besides far harbor, my beautiful baby boy