Oh god... you want to willingly step into that? Because that series has been the epitome of disappointment for young-me.
Well, I guess you at least can come into this without the built-up expectations that Peter Molyneux plants in people.
Start with the Lost Chapter version of the first one, it's probably the best both mechanically and story-wise.
The second one is the one I hate most. It is so incredibly vile. It doesn't give a rats ass about logic or roleplaying or choice and has probably the two WORST creator pets in existence, not to mention how carelessly they treat the dog - you just don't build up any relationship with it. Just avoid it, you won't miss much. Mechanically, it is incredibly broken since any ranged-magic hybrid style essentially wins you the game.
The third at least fixes a bit of that, making fights a bit better. Storywise I actually liked it more than 2. A lot more. Maybe just because it has a clever twist. That twist is horribly executed from a mechanics standpoint, but at least it sort of makes sense and is built around your character instead of the creators favourites. And it kinda handles the dog part better - i.e. you actually might feel something for the guy.
So, overall, my advice is to start with one, skip two and then take three.
I do advise you to crank up the difficulty though - only the first one can be a challenge, and even then only because of how clunky it is at times. I think I have never even once seen a game over screen or had to use a Vial of Resurrection in any of the Fable games.