Reaching semi finals is something few people ever get to reach. I think the best of 3 is not the best strategy. Not the first time i feel like i could have turned the tables on my semi finals.
I'd say make it best of 5. Only 4 teams ever reach it and we should assure the best team gets to the final. I've seen many games turned from 2-0 to 3-2. If you have bad luck on the first map and it happens to be your map, you are doomed to lose the other because its the other team's pick.
My opinion as a guy who has played best of 5's and best of 3's.