We did the excursion to Meteorola. While the 2 hour bus ride was a bit long, the views from the cathedrals' built on 200 foot high rocks was fabulous (and well worth it). Highly recommended. Also had very nice buffet lunch at a hotel / resort with views of Meteorola (one of the best meals we had on the trip).
We went off on our own here which I would recommend as very doable (don't bother with the $5/way shuttle, not a far walk). Nice Cathedral, very cheap shopping and nice old town/pedestrian area full of dining/drinking/shopping options. We also spent time on a very nice beach in town. Swimming in the Black Sea is recommended (quite refreshing, much more lake like than ocean like in terms of salinity).
Note that we also heard several complaints from people who took tours from Easy Varna to Nessebeur (sp?).
We love Istanbul, but have spent time here before, so we opted to visit on our own. Seeing Topkapi Palace (very nice architecture and views) and then touring around a bit on our own. Be prepared to bargain for pretty much anything (there is a reason that even trinkets like magnets do not have prices on them).
Our tablemates did the Elite Istanbul tour (actually by mistake, checked the wrong box) and loved the tour (this was only one of two tours on the cruise that they had much positive to say and they took several).