There seem to be a lot of good information about different BC's on this thread so, I'll through in my $.02 in a slightly different direction.
Before you buy, talk to the staff at your LDS. Explain you questions and see if you can't exeperiment with rental and their gear. I work at a shop in STL and we handle questions like this everyday. There are certainly pros and cons to each style of BC config all of which a have been explained pretty well here. But you will never know what is best for you until you try. We let people use our gear all the time in the pool, just to try out different styles. Its a great sales technique and it allows the customer to get what they want the first time. You'll probably find that your LDS will be willing to help in a very similar fashion.
Before you buy, talk to the staff at your LDS. Explain you questions and see if you can't exeperiment with rental and their gear. I work at a shop in STL and we handle questions like this everyday. There are certainly pros and cons to each style of BC config all of which a have been explained pretty well here. But you will never know what is best for you until you try. We let people use our gear all the time in the pool, just to try out different styles. Its a great sales technique and it allows the customer to get what they want the first time. You'll probably find that your LDS will be willing to help in a very similar fashion.