Well its entirely your choice, I would suggest though to choose a project (or 2) and stick to it for a while. Whether it is the U-boat game or NinjaCat or both doesn't matter much, both seem to have potential, just don't begin on a new project after e.g. a month. Cause otherwise your projects would be half-completed at best and would just rot away somewhere since it will be not finished enough to for you or for others to play it and probably not interesting enough to pick it up again.

At the time when I made my first game(s), I was constantly switching between projects, resulting in more than a handfull games just being garbage. I learned alot from it, but its still a waste otherwise it would have definitely added about 2-3 extra (mini)games to my games list .