I don't know about "2-man best ball" (maybe you're playing 2 teams in a foursome?), but "best ball" is when everyone plays their ball from what's judged to be the best position. Saves a lot of time if you're a hacker, like me. But if you're a stubborn hacker, like me, you try to play it from whichever patch of rough you launched it into. I did know what scramble is, but now it slipped my mind.
JDL: From one Minnesotan to another: Welcome to GolfRewind!
As I understand it, 2-man best ball works this way: You and your partner are a 2-man* team. Each of you plays your own ball for all 18 holes. At the end of each hole, whichever one of you has the better score, that's the score for your team on that hole.
As I've played scrambles, the entire foursome is a team. Everyone tees off. One player's shot is deemed best, so the other 3 pick up their balls and bring them to the other guy's ball. All players then hit from that spot. Repeat process until hole is completed. A scramble can also be played in teams of 2 or 3. So, if you and I were a 2-man scramble team. After you split the fairway long and I slice my tee ball into the rough, I humbly bring my ball to where yours is and we both play from there. Repeat till hole-out.
According to The Rules of Golf, Best Ball is "A match in which one plays against the better ball of two or the best ball of three players." Thus, there is no such thing as "2 man best ball." You are either referring to a match between two players, which is called a "Single" or a match between two teams of two players, which is called a "Four-Ball." :)
Speaking of scrambles, did someone watch the Michael Douglas charity scramble after the British Open on Sunday? On the final hole (par 5), the leading group with Yanni (a pretty good golfer with a range and swing analyzer in his home), Joe Pesci, Tom Arnold and Heather Lochlear were on the green in 3 shots but still pretty far. Heather was last to putt after everyone missed and made the birdie for her team to go up 2 shots. It ended up being the winning putt. That's what makes scrambles fun. Everyone on the team gets a chance at making those "clutch" shots.