I usually play flatwound strings. They've always been my go-to string for the sound and feel, and I love them. But I'm in a bit of a dilemma because I'm hitting the road down to Austin for SXSW about this time next month, and I'll be playing straight up Rockabilly. I usually play more of a smoother western swing, so I like the flatwounds. I feel as though I should go for roundwound strings because the brighter and spankier tone that follows them.
What would you do?
Use whatever is most comfortable and easiest for you to play. Rockabilly guitarists have used both rounds and flats.
If you're playing for a rockabilly crowd rest assured 99.9% of them will be more into dancing and making the scene than what type of tone you get out of your guitar.
I love TI flats on my Falcon, but they didn't sound as full on my Corvette, but since I hate the feel and 'squeek' of round wounds.... I tried a set of GHS 'rolled' wound Nickel Rockers, (Eric Johnson 11s). My favorite strings now on the 'Vette!
Adjust your amp and guitar treble settings to see if you can dial in what you want. Just my .02 as I dislike round wounds also.
Didn't Cliff Gallup use flatrounds ? Can't get much more Rockabilly than that..
I use Thomastik-Infeld .011s on 4 different Gretsches. 3 of them have flats, 1 has roundwounds. The big difference -- the roundwound set has a plain 3rd string, which is much easier to bend. I am strong enough to get a whole step bend out of the flatwound 3rd, but it takes about twice the deflection (distance of the bend across the fingerboard) as the plain 3rd.
Point being, if you can physically execute everything that you want to with the flats, stick with them. Better to go with what you are used to and comfortable with. Captainvideo is right that you can get an absolutely appropriate rockabilly sound with flats, and no one but you will notice if you do go with the rounds.
If it feels good do it.