Finn's are everywhere at the mo and have been for a few years. It's a lovely name so that explains it but it depends if popularity bothers you. Flynn is also lovely and not used so much.
I met a baby John recently and it made me realise that I haven't heard a baby called that in years! I really liked it and it really seems to suit him.
I like Flynn as a first choice (even though you didn't include it as an option 
) and then John with Finn last.