Flo is a much trickier player than Youzhny, that's for sure.
Entirely depends on the match-up - Flo doesn't give you much rhythm, but Youzhny has a lot of big match experience - he doesn't match-up well with Fed, but has beaten Nole several times (as well as Nadal, and at a slam). I love both, but this is perhaps only the second good tournament result Flo has had this entire year. Both are very good grass players - however, Misha is the better player. Plus, Youzhny's wife just gave birth last night, apparently?
Both are dangerous players and have weapons though, for sure.