Flats will dry quicker than prefolds because the prefolds are layered down the middle.
Bamboo prefolds are better for long term use as a booster later on. Cotton wouldn't cut it with toddler wees! I made them 30cm square and they worked brilliant for Ruby as a newborn and I use them in Calebs pocket nappies now. Well I did

Flats have their pros too though and make great burp cloths and I always have a spare one in the nappy bag for change times as II'd rather wash one of them than the change mat.