I highly prefer Bo3, because it actually gives us a winner, instead of a tie.
The main reason I absolutely despise Bo2? The completely arbitrary point structure. There is a reward for winning a Bo2 set, but NO punishment for losing it.
Exhibit A: We have 2 teams, Team A and Team B. Both of these teams have played 10 Bo2 series (not against each other), and each have won 10 games and lost 10 games. Both are .500, both are completely average, both are EQUAL. But wait! Team A went 2-0 in 5 of their matches, and 0-2 in the other 5; while Team B went 1-1 in all 10 matches. This leaves Team A with 15 points, but Team B only at 10, despite both teams winning and losing the same amount of games.
Team A was rewarded an extra point for winning the series - instead of 2 points for winning 2 games, they were given 3 points because they went 2-0. However, when Team A went 0-2, they still received 0 points. They weren't punished for losing, ONLY rewarded for winning.
This is how things work in the current Bo2 format:
Whichever team wins game 1, they get 1 point. Simple, obvious. The issue comes in game 2. Let's say Team X won game 1. If they win game 2 as well, suddenly that game is worth 2 points for them, instead of only 1 (because if Team X wins game 2, they are given 3 points for winning 2-0). However, if Team Y wins game 2, then it's only worth 1 point to them (because each team would go 1-1 in the series). How can the same game be worth a different point total for each team?!
In a Bo2 format, 1 game should equal 1 point. Winning a series should be worth 2 points, not 3.