I think you'll rarely go wrong giving away small useful programs as free software. It's the easiest way to get users, and once you have users you'll learn even more about how to make the software better. If you're lucky you'll find other people who want to contribute, and you'll get a chance to work with them and meet them. And an original free software project is a great thing to be able to show off. If it's indeed a small amount of effort to duplicate, then there's probably not that much selling opportunity that you're giving up.
If you do a good writeup and post it to Hacker News and Reddit, you can probably get some good feedback and a little notoriety. I got some really helpful comments that way on my last little useful project.