I found both my Princess cruise and HAL cruise had super great shows. the food was excellent on both too-although I found HAL preety subdued-once the show was over-there was no entertainment-the lounges were dead-now Princess was better-but things did close up around 1 a.m.-but that was fine with me as I "close up" around then myself.
Now on RCCL-I found the shows just okay on Sovereign but much better on Mariner.
I have been on 4 Carnival cruises and found the shows decent, better then on Sovereign-but not great-exept for Carnival Miracle-the shows were superb on her.
Disney had good shows too-but they were Disney themed-not Las Vegas style-if you have ever been to a Disney Ice Show-they reminded me of that-exept ofcourse they danced and sang instead of skating and siging.
But I really thing it is not the line but the ship-newer ships have the best entertainers-and when you go more upscale on the cruiseline-the shows are better too. Makes sense to me-the more you spend on a cruise-the better the shows will be.