I'm a fan of rounds, flats, tapes, and halfwounds.
Still, the VAST majority of bassists prefer rounds, so rounds are what come stock on most instruments.
When I bought my Squier VM Fretless Jazz, the shop had already changed the strings to TI Jazz Flats, which was pretty awesome.
As for the genre deal, I was speaking to a bassist lately, between sets at a bar gig, he was playing Irish music, with a real fat, thick, deep, smooth tone, total buttery reggae tone. He was playing a Trace rig, with a Stingray(pre-EB 2-band red/maple, fwiw), and rounds, told me he just can't stand flats. It was really odd, but dang was it incredible sounding.