You don't need to have a background in either of the sports.
I rowed (actually I was a coxain b/c I'm small aka short) for my first semester as a plebe, then tried power lifting the following semester, and final found my home with the Intertnational Sports Pistol team and D&B (I did both at the same time). Crew is tough, but a great work out - plan for EARLY morning practices. Just do something that you enjoy!!!! It's always nice to be able to earn your Varsity 'N' letter so if you can participate in a varsity sport do so, in the end do something fun that you enjoy!
Being invovled in your company is overrated. You got selected to attend the Academy because you are a "well rounded" student. The fact that you get "graded" on your FITREPS b/c of your time spent "in company" is ridiculous. I was actually told I was ranked below someone b/c I chose not to drink with my company.
That is NOT how things work in the Fleet and that is NOT how your rank your Sailors either. You take all things into consideration, involvement within your division, department, command, community, etc...
anyway, I'll get off my soap box