I have had the chance to both of these cruises on rccl and can tell you the the abc route is much better for not only you but the people traveling with you. If they choose to snorkel it is much easy on that route also the towns have a few more things to do. Costa maya is nothing more than a market, this may have changed as its been two years since I was there. A couple other things to think about I was able to get on dives with no more than eight people in a group on all abc stops booking on my own. Coz has many ops so this is not hard. There were only two when I was in costa so that makes it much harder. I could go on but its a lot of what you will already get. If you would like any detailed info on the ships or opps I used feel free to ask.....