G1, G2, G3, G3.5, G4
I think G2 and G4 look the best IMO.
I love FiM, but in toy form they look like elves.
I like G3 and G2 the best in terms of toys. Sorry G1 ponies, I love you all, but y'all is too damn fyat.
Now, in terms of animation, I overall dislike G3's cartoons. I still watch them sometimes, though. As it is my childhood.
I love the FiM cartoon, obviously. But I prefer G1 more, whilst FiM is better in terms of a lot things, especially character development. I mean, the G1 characters were really cool. But they didn't have much personally, and they just had almost no feeling to them. In FiM you can actually feel for the characters.
Though G1 did have a high fantasy feel to it and it had an oddly dark aspect to it. And had much better villains. Don't get me wrong, I love Discord and Nightmare Moon, but they aren't scary. Discord is awesome, but he's more like a joke(I mean that in the least negative way possible) than anything.
The G1 villains were downright loving scary. They terrified me as a kid.
And plus, G1 one was one of the least girly generations.
I've been heavily addicted the 80's cartoon again ever since I found an old box set.