I only used round wounds for over 20 years, but the last couple of years i've been getting really into flats. That said, not all flats are the same.
The TIs on my Epi Jack Casady are very musical rather than thuddy, but low tension. The Labellas 760FLs on my Precision are very beefy and smooth, but not particularly high tension at all (i.e. I can still do two-fret string bends pretty easily).
That said, I've got nickel rounds on my Lull which sort of suits that sort of bass better....