You don't buy a bike by the size of the wheels. You buy a bike by the size of the frame. You should go to a bike shop and let them show you what size bike is appropriate for you. The importance of doing this can't be understated. A properly fitted bike is a joy and pleasure to ride. A poorly fitted bike can be torture. If you go to a bike shop and they tell you what size to buy, don't feel obligated to buy a bike there. They should compete for the best value for the kind of bike you want to buy. Besides, if they are the closest bike shop, you will be back to buy tires, tubes, clothing, and other accessories. I have hear they make more money off that stuff than they do from the bikes.
Note what I've said about where to go. The importance of going to a local bike shop bears repeating. They have people who are qualified to match you up with the bike that best meets your needs. Big box stores don't have those people and their bikes are not worth riding for more than 10 minutes at a time.
HTH