photo credit: richardmasoner
Female athletes interested in performance have their choice of road bikes, time trial bikes and mountain bikes specifically designed for women. Depending on the intended use, components and budget, sport-specific bikes can range from $300 to custom bikes in the tens of thousands. Women interested in casual, non-competitive riding also have many options to choose from. There are plenty of hybrids and comfort cruiser bikes for women to choose from. Now that bike-commuting has become popular, city bikes for women are also becoming more common.
There is no one "best" bike for women - it depends on the type of riding she will be doing, her fitness level, and her budget. Some bikes have the capability of being multi-sport bikes (for road, mountain and city riding), and some are very specialized (such as time trial bikes). If the cyclist has the budget for only one bike, it should be a bike that "does it all". Hybrid and city bikes are probably the best for all-around use. Although they are heavier than road bikes and not nearly as aerodynamic, they are comfortable and can be light enough to ride long distances. Some hybrids are quite heavy and designed only for bike path use; however, city bikes (which are a more road-worthy cousin of hybrids) are more and more present on century rides (100 mile rides) because of their comfort. Hybrids and city bikes are not designed for aggressive trail use, but can easily handle gravel roads or gentle hiking trails if the tires are switched out to knobby cyclo-cross tires for better traction.
Comfort bikes for women are popular with cyclists looking to cruise the bike path or ride around the neighborhood. They are strictly for fun - they are not nimble climbers on the hills, nor maneuverable and responsive as road and mountain bikes, but for a fun, gentle ride that does not blow the budget, they are great.
Although most women's bikes fit most women, there are a few out there who are particularly short, or tall, or have certain physical requirements, that are not addressed in "off the rack" women's bikes. For these women, custom bikes can be an alternative. Expensive, yes, but worth it when their personal requirements are met!