Female sportsmen considering performance have their selection of time trial bikes, road bikes and mountain bikes made specifically for girls. According to parts, the planned use and budget, sport-specific bikes can range to custom bikes in the thousands. Girls considering casual, non competitive riding additionally have several choices to pick from. There are lots of relaxation cruiser bikes and hybrid bikes for women to pick from. Since bike commuting is becoming popular, city bikes for girls will also be becoming more common.
There's no one "best" bike for girls - it is determined by the kind of riding she'll do, her level of fitness, and her budget. City and hybrid bikes are likely the best for all around use. Although they may be heavier than road bikes and never almost as aerodynamic, they can be light enough to ride long distances and are comfy. City bikes and hybrid vehicles aren't designed for competitive trail use, but can readily manage gentle hiking trails or gravel roads if the tires are changed out to knobby cyclocross tires for better grip.
Relaxation bikes for girls are popular ride around the area or with cyclists looking to cruise the bike trail. They may be purely for interesting - for a fun, light ride that will not blow out the budget, they can be excellent, although they aren't nimble climbers on the hills, nor receptive and maneuverable as road and mountain bikes.
For these girls, custom bikes can be an option. Pricey, yes, but worth it when their private demands are satisfied!