In absolute terms, Becky, a road bike is the way to go. Its more aerodynamic than a cross bike, and the drop-style handlebars afford you a greater variety of hand positions so that youre more comfortable on long rides.
Giant FCR 2 bike
FCR 2 bike
But life is relative, not absolute. Road bikes have their disadvantages, especially if you havent ridden one before. In short, they can be dreadfully uncomfortable due to the hunched-over riding position. So you have to take that into consideration.
In a cross bike, I like something such as Marins Lucas Valley (US$800; www.marinbikes.com). Its a fast cross bike, with a light aluminum frame and road-style tires. But its also got the slightly upright position youre accustomed to on your mountain bike, and a triple chain ring for hill rides. Also, it can take light touring gear, so you can put on fenders and some racks and spend a few nights on the road. Giants FCR2 (US$650; www.giant-bicycle.com) offers a similar package in a bike thats sized and fitted for women.
You might also look at a touring-style bike. These have road geometry with a slacker frame for a smoother ride and typically offer a little more upright seating than a true road bike. Treks 520 (US$1,200; www.trekbikes.com) is a classic of this type, with a comfortable aluminum, upright stem so youre not crouched over but are still fairly aerodynamic. It has lots of places to attach fenders and racks, and gearing thats well-suited for long rides. Its an excellent all-around bike.
My advice: Test a few different bikes to see what feels right. Try to persuade the shop to let you have five miles or so on the bike, so you can really get a sense of how its going to feel after more than a few minutes.
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