I think both have their good and bad points. Milepoint has a better interface and I like the avatars but what I don't like are the status points. I was actively posting there for awhile, then it got ridiculous with people begging for "likes" or posting anything just to increase their status. What I don't like about FT are the mega-threads. These programs change so often what was relevant a year ago probably isn't relevant this year. At least some forums start new threads each year like the IHG forum.
I also don't like when airlines are merged but they keep separate active forums on the old programs. A good example is old United, Continental and the current merged program. I get that some people are unhappy with the merger but it's a reality and they have to deal with what it is, not what it was. I wish they would relegate the old forums to historical archives and make them read-only and have everyone post new topics in the current United forum.