Hi Hilary and welcome to the forum.
The beauty of a JY holiday is that you won't be on your own. It's natural to feel apprehensive your first time. I think it's best to pick a location which you've always wanted to visit which will help in the run up to the holiday. The admin staff can tell you how many people have booked a particular holiday, what ratio male to female and what age range. If you are looking for May, I wouldn't delay as a lot of holidays have been fully booked already (they disappear off the website when full).
Good luck with deciding which trip to pick.
Sally