D'Addario Chromes are great flatwounds; they have the most "growl" among the Flatwounds available.
I've been using D'Addario XL's (nickel rounds) for years, and I'm quite happy with how long they last. They definitely keep their growl longer than most others. I have recently tries GHS Boomers, Rotosound 66s (both didn't last as long as D'Addarios), and DR Black Beauties (good strings, but not exactly my sound). Still on the try out list are D'Addario EXP's (coated rounds), and maybe Sadowsky nickels..
TYMC has good prices for D'Addarios.