We chose RCCL Serenade of Seas due to the itinerary in the Baltic and St Petersburg. In our case we picked our general travel period, ports and then cruise line. I spent probably 40 hours total reading and researching every review I could find on who to spend the $$$ with as Scandinavia/Russia are not inexpensive places to visit. We decided on a suite,(GS Category) cabin #1052 with concierge privileges. It priced out better than the other higher end cruise lines running similar itinerary. (They offered a 3rd day in Russia but the $$$ difference was staggering.) I liked the size of this ship and found it clean, well cared for and appealing for such an adventure. Even though we made the ship choice our 3rd criteria we were thrilled that it all came together perfectly for a lovely trip.
I found the food to exceed my expectations (as I had thought it was only average on an RCCL transatlantic two years ago). It was excellent on this cruise, nice variety and very good service. The specialty restaurants (we did all 3) offered a more intimate experience and we enjoyed the Italian restaurant the most. We liked that there was fresh fruit, vegetables, seafood, etc - available every day no matter which dining venue we decided on that day.
We did our tours through SPB and visas are NO issue. I would use them again and I think they absolutely are the St Petersburg experts.
Quite, perfect location, many drawers and unpacking spaces, well designed to set beds away from couch and bar - we really liked this as we are two friends not a couple. It gave each one of us a nice amount of "living" space and it felt like a mini/mini apartment.