I also used to dislike
Jack due to its popularity, but it's my boyfriend's favourite name (guys seem to really like the name
Jack in my experience!) so I started to re-think how I felt about it, and now I love it and it's currently our top name for a boy.
I definitely prefer it as a full fn, I'm from the
UK and it's never really used as a nickname for
John here nowadays. It's really popular here too, but I think it's popular for a good reason. It's strong, snappy, cool and unpretentious and it also has a lot of history- some people might say it lacks substance but I don't think that's true. I like the fact it was very popular during the Middle Ages and was used in a lot of fairy tales and nursery rhymes (
Jack and the Beanstalk,
Jack and
Jill,
Jack Sprat etc.) Wikipedia says
Jack was a folk hero:
http://en.wikipedia.org/wiki/Jack_%28hero%29
Theodore is nice, but a bit too heavy sounding for me. I do like
Hugo and
Conrad, and I think they both go well with
Jack. I've never liked
Ronan as it just reminds me of
Ronan Keating the singer.
Kepler is quite interesting, but not my style. I think it's usable though and doesn't sound too girly.