We purposely book a Reserve Collection mini-suite or higher category when we cruise with Princess, which as of late is quite often. We just enjoy showing up to the dining room for breakfast, lunch (on sea days) and dinner, being escorted to our same table (since we don't need to sit near a window), attended to by the same wonderful servers, and of course enjoying their tasty meals, which are always served hot has they receive priority service (from our understanding) when fetching our selections back in the kitchen.
As far as comparing the Reserve dining room with Celebrity's Blu, which we also frequent regularly when we cruise with them, the Reserve wins hands down, along with the fact the Reserve is open for lunch on sea days whereas Blu is not. But I will also note, we are usually there for dinner when they open at 5 pm. If you like to eat later, say around 7 pm, it might be a little more crowded depending on the part of the world you are cruising in.