We've been on both and have enjoyed them both, although only once on Crystal. Cabins on Regent are definitely bigger, and although assigned dining isn't a deal breaker for us, we have come to enjoy the open seating on Regent. We also like the smaller number of passengers, although again, 900 versus 700 (or even 400 on Navigator) wasn't a major difference, we enjoy getting to know our fellow passengers and seeing faces we recognize.

I think you will enjoy Regent and be very plesantly surprised honeymooner's, and you will find some very similar things as well, tea in the afternoon, good food, nice, plesant, accommodating staff, interesting, well traveled fellow passengers, etc.