Both are excellent
I have never owned a Thompson, so I can only comment on the Raceface posts.
Daibolus is heavier and capable of accomodating much more serious seat post angles. The two bolt design causes the sadle to almost never move. This is a very good thing. Seat posts like the XY tend to suffer from the saddle rotating if you land really hard on the back of the saddle. Syncros posts would break from this. I know that Thompson posts have excellent reliability and I can't say if they would break or not under this type of severe loading. They may be totally fine.
However, the diabolus has the advantage that it WILL slip. It has to be a really, really hard hit for this to happen, but it can save you from a broken seat post.
Really, there is not too much to dislike about either seat post. Both companies have great reputations and generally make solid products. I have been using the Diabolus posts for just over a year now, and really, like them. My only complaint is that they are short at 350mm - this seems to be a trend in the seat post manufacturing world; I would like it if it was offered in a 400mm length.