Are you limited to one practice area? Many firms have rotation systems, where you can do a variety of things in both litigation and transactional practice. Some firms have a project based system, where you choose from available projects. With both of these systems, I'd try to get as much variety.
If not, then I'll give you a summary one of my professors gave re: litigation and transational work that might help you: Transactional practice is about building a deal, and creating something. Litigation is about dissecting it after that deal has gone wrong.
They're slightly different types of problem solving, IMO. So I'd think about which appeals to you, and then give that a try! And don't stress too much about it. It's 1L summer, and you're expected to be trying things out. If you don't like what you chose this summer, then you'll be absolutely sure what practice area you're looking for during the 2L job search!