Our four prior cruises were on Princess and we booked this one on the spur of the moment (2 weeks advance of departure date). On Princess we were on the Golden, the Sapphire, the Ruby and the Diamond; all beautiful ships.The first thing we did was read Cruise Critic (CC) reviews; since we really enjoy the food, we were concerned that there were so many reviews that really blasted the food quality; but we wanted to see for ourselves.This was our third Mexican Rivera cruise and we did it because the main thing is the cruise experience, so we did very little onshore, other than hook up online at an Internet shop and a short boat ride around the Cabo arches..So here is my/our take; remember, we only had Princess as a comparison.PROS:For the most part, we found the food quite good; but we have to say we are not gourmet eaters. The baked goods in the Windjammer buffet were much superior to those in the Buffet on Princess. Our RCI balcony stateroom was very large and we really appreciated the sofa; we understand even interior cabins have sofas.Entertainment was really enjoyable and the ice show was top quality; entertainment here was much better than Princess and that may be because it is aimed at a different "crowd."  We did love the presentation by Libbie Riddles (live) who was the first woman to ever win the Alaska Ididerod race.Much more onboard and diversified things to do than on Princess; loved the rock climbing wall (even putting up a youtube video of old me doing it), as well as the miniature golf and the game room; we also enjoyed the parades and Captain Johnny is a hoot; good sense of humor.For coffee drinkers, the "Seattles Best" coffee was better than excellent plus; best on any cruise.We liked the "adult only" pools and spas very much.Both Princess and RCI staff were very helpful, friendly and did a great job. CONS:We didn't care for the assigned seating as we enjoy "Anytime Dining" on the Princess; we were stuck (having booked at the last minute) originally with an 8:30pm dinner time  that for us is way too late. We ended up doing two specialty dinners (extra cost at Chops and Portofino's) and we found them both to be excellent plus.  We were however able to get reassigned to a 6:00pm dinner, but only for three nights.I really didn't like the mandatory "gratuity" if we didn't take an assigned dining time; maybe it's just semantics, but I don't like it to be called a "gratuity" when it's mandatory.Internet costs are very high, but less than Princess.There was what could have been a major disaster glitch in organization whe departing; we were on the last group off and were told to meet at a specific place; we went there and it was locked up with no instructions on wher to go. We we lucky to catch a crew member who said we should just depart "over there" and that they were always printing the locatoin that was not open; had that crew member not been available, we possibly could have missed our transport to the airport; it was the last one out. MISC.One thing you may want to consider, and that is you can save a lot of $$ if you book your shore excursions privately when you leave the ship; we saved half on our Cabo boat ride (and it was much more personal) over the pre-booked one offered by RCI (and same for those on Princess).A lot of people say they don't like being "nickle and dimed" for so much stuff, but I believe in a "user pays" attitude; we don't drink soft drinks and many other things that are extras (added charges) so we don't like the idea of having the overall cost of the cruise raised to cover things we don't use or want.A much younger and family/child oriented group than Princess, which was not a problem for us other than occasionally parents who seem deaf and blind to how their children are acting onboard; I really wonder if these parents would let their children climb on the chairs at home.We found it very interesting that if we booked direct with RCI, there was no onboard credit available to us; but if we booked through "Smart Cruiser" we got a US$146.00 onboard credit after a US$29 fee for joining Smart Cruiser (as I recall).The Mairner is absolutely gorgeous; with the Royal Promenade made the ship the most beautiful we had ever been on in our limited experience; but this is not to put down Princess ships that are beautiful in a different way.And not to forget; we saved half the cost of the RCI shuttle by taking the Prime-Time van from LAX righ to the ship (and that's serious money), since we didn't use all our onboard credit, we used it to get back to LAX (since it doesn't carry over to your next cruise on RCI).We were very surprised and disappointed that the TV had no A/V or S-Video inputs so we could watch our own DVDs; don't know why this is.The RCI "Meet and Mingle" gathering (supported by CC?) was nice and RCI even gave the group a venue for almost an hour to meet and mingle, including snacks and a drawing for prizes; a nice added touch.We were glad the Art Auction and photos were not right in-our-faces on RCI.It may seem from this review that we prefer RCI over Princess but that isn't really true; each of these lines cater to a particular target group. The background music on Princess is much more "reserved" while on the Mariner it was very upbeat (and louder).   Living in Mexico has to some degree taught us to go-with-the-flow and enjoy the day; we didn't look for negatives on either line and did look to enjoy each day; a lot of it has to do with attitude and we try to maintain a positive attitude and not let the topas (bumps in the streets) be prolems.Would we book RCI again? Yes. Would we book Princess again? Yes. Will we consider other lines? Yes (but probably not Carnival).