Yeah I prefer MLB because that's the focal point of the defense. The MLB is in position to make plays on any snap...you can drop back into coverage, defend against the run, pass rush (although I never blitz anymore with Beason just to avoid any questionable nano-blitzing issues), etc. etc. I tend to choose primarily LB spy plays in order to basically have free reign to do whatever I want on the field. I don't like to be committed to one player (i.e. man-to-man defense) or one area of the field (i.e. zone defense). I basically like to scour the whole field with Beason...although I obviously can't cover the deep routes as effectively, so I basically stick with covering short and medium routes.
I've never tried playing with a safety or CB, but I don't think I'd ever want to switch. I definitely wouldn't want to play CB cause, like I said, I don't want to be committed to defending one player all game. I feel like that would be pretty boring for the most part...and you would only be making a direct impact on passing plays where the QB is throwing it to the receiver you're guarding. I think safety would be fun too, but safeties play further back and aren't in as good of a position to defend against the run, so I just stick with LB. I might consider switching to safety against players who partake in a pass-heavy offense or players who like to throw the deep ball. Like the game I just had with the Colts (who were taken over by gregthomas)...he ran one run play the entire game lol, so I ended up with a very unproductive game with Beason (like 2 tackles...). It would definitely have been more efficient to play safety that game...
I agree less advanced defensive players would be better off with DE or LB, but I don't think playing Safety would be any harder than those two positions...it's basically like playing a linebacker in zone coverage, just deeper in the field. CB's on the other hand are definitely reserved for good defensive players...I feel like the person you're playing against could easily exploit your coverage if you were playing CB. There are a ton of tricky routes with players cutting inside for like a second and then immediately running a streak route or something like that. If a speedy receiver gets even one step on you, then you're pretty much screwed.