As to the cabins in O vs. R, my vote goes to Regent. When planning my first cruise as an "upgrade" from Celebrity, I compared costs for a Regent Explorer Concierge D vs. an Oceana Riviera (sister ship of Marina) Penthouse. The cost was close, so we opted for the Concierge D on Explorer (and I am glad we did). Our next cruise was on Riviera, in a PH. Although the size of the cabins seems similar, the layout of the concierge suite on Explorer, including the much nicer/larger bathroom, was much better than on the Riviera PH. Another major difference was the balcony, which was larger and deeper on Explorer. As to food, we really enjoyed Oceania, especially the French and Italian restaurants, which were better than on Explorer. We were disappointed with the main dining room on O, as none of our meals there were anything of note -- just mediocre as to quality and taste. For lunch on O, the Waves Grill (pool grill) was open, although the burgers and other items on Regent's Pool Grill are better. After the O cruise, we went on a Splendor cruise (which was better than our first Explorer cruise) and decided that we would stick with Regent thereafter. We just disembarked from a Mariner cruise last week, which was our best Regent cruise so far. Although impossible to describe, and it being an individual choice, we enjoy the "vibe" on Regent over Oceania. A major bonus, as you mentioned, is that there is no need to show your card when getting drinks on Regent.
Jerry