Best Cruise to take for 1st time cruise, special requirements if 1 of us has a passport from a foreign country

Question

My husband and I are thinking about a cruise for our 5 year anniversary. Would like to know what would be best for late 20's couple, no kids yet. What ship, best place to go? Also are there special requirements if one of us is a u.s. citizen (has a u.s. passport) and the other is not but has appropiate documentation (i.e. home country passport and re-enterence documentation) Suggestions? Thanks!!