We did a Baltic cruise on the Oceania Regatta in June 2009. We chose this particular itinerary because it spent an extra day in St. Petersburg over most of the other cruises we saw, and because we had been on two earlier cruises with Oceania. We enjoyed the cruise very much, but did not use any of the ship's tours and instead arranged private guides with other passengers which we arranged through roll calls on CruiseCritic.com.
Booze is not included on Oceania, but they have a somewhat liberal policy about allowing you to bring on board your own liquor and drink it in your cabin. Although we have never been on SilverSeas, we know Oceania is a step up from Royal Caribbean and comparable lines. We enjoyed the size of the Oceania ships we were on, which all hold around 700 passengers.