If you're able to, I'm always an advocate for new. The boat is 100% perfect(if not, they're going to fix it), the motor hasn't been touched by a shade tree mechanic, and the trailer is brand new(tires, hubs, lights, etc.) This has always given me peace of mind that everything is going to work for a long time and it will be maintained to my expectations from the beginning. I'm a big advocate of maintenance, which will bring more reliability. I know things break down eventually, but I'd rather not be stranded in the water with the wife, friends and kids.
I have bought used as well. I had good experiences going that route. Bring a knowledgeable friend to help you look around so the new to you "wow" factor doesn't blind you from overlooking anything. If it's a high dollar purchase, a couple hundred bucks for a survey/maintenance checkup is not a bad idea so you know what you are getting from professionals.
Good luck with you decision, it will be one of the 2 best days of boat ownership!