Hi Hummelcruiser. When you're choosing between Regent and Crystal, you can't really go wrong either way.
Regent carries fewer guests on board, but the ships are a bit smaller so you'll have the same sense of space on either line. If you drink alcohol often, then Regent may be a better value because it is all-inclusive. Regent also offers on many of its ships all suite, all balcony accommodations. Crystal, though, was just rated best overall cruise line for the 14th straight year by Conde Nast Traveler, has great onboard entertainment, and offers a lot of complimentary enrichment programs.
They are both terrific cruise lines. You also can frequently find agencies that are offering pre-paid gratuities on Crystal. When you book into a Crystal cruise offering prepaid gratuities, you take this additional expense out of the equation when comparing the two lines.
At the end of the day, it may come down to itinerary for you. Which cruise line offers the itinerary on the date(s) that you want to travel.
Have a great birthday!