I totally agree. We have cruised Carnival three times with our fourth coming up in December and for the most part have had only positive experiences. After our upcoming cruise we're going to switch lines just so we can judge for ourselves if other are that much better.
I do agree with the statement about TA's not wanting to book people on Carnival over their commission .
I think Carnival gives you a great bang for you buck and am not too sure if every higher price line are really worth the cost when it comes down to it.