Finishing your repair is a very satisfying step in the process. It is the most visible aspect of your the work. It doesn't matter if you have made the most structurally sound repair. If the final step doesn't look good, the work doesn't look good.
Leaving your repair looking good - or better yet - being undetectable - is probably the most difficult part of fiberglass boat repair. Small goof-ups in this stage are difficult or impossible to mask.
In short, one-part paint is the easiest to apply, but it is difficult to hide mistakes. Gel-coat is more difficult to apply, but it can be sanded and buffed to remove application errors.
Two-part paint is expensive and difficult to apply properly and safely. This product should be left to the pros!