I agree that there's a deeper connection with the LF characters. Especially in the LF series the player experiences an emotional rollercoaster with them. All the effort they put in their quest, yet all the failures ... And then some really tragic moments (like poor Sandy which literally made me cry

).
Yet, though I really like MM and despite the fact that there are already 4 games, I never got that kind of connection to its cast. Maybe because not all of them stayed with Marine all the time, I don't know.
Last but not least TBOL. Yes, one game only. But oh, what a game! And the characters are very unique! There are characters who are adorable and such I don't like. Which I mean in a positive way because it's more life like.
Again it's the choices in the game that make the cast even more interesting.
First and foremost ... killing Jasmine!? We've been making fun in the other thread about this, but seriously, it was NOT an easy thing to do. Killing a cute little girl (12 or 21, who cares)?
Then, when choosing the school, you have a close look at all the characters that might join, before making a decision. You pay much more attention than when they join anyway.
For me the characters in TBOL have more personality than in MM.
So to sum it up:
MM is in second place for me, TBOL and LF share the first place.