By request, the Top 100 ranked characters in 2v2. See the FFA chart here: http://community.us.playstation.com/t5/PlayStation-All-Stars-Battle/Top-100-Chart/td-p/39333035
This chart shows how many times each character shows up in in the top 10 ranked players, then top 20, and so on. This does not include players that were high ranked but had no scores. The accuracy of the leaderboards overall should probably be taken with a grain of salt.
It is important to realize, a chart like this cannot distinguish if a character is simply (un)popular or unbalanced.