The amps I had initially crossed off my list were just because I tried the wrong version/revision and then I learned better (like with some Diezel's, Recto's, Wizard's, Soldano's and others)
I also didn't like some of the vintage NMV Marshall's super leads I'd tried in the past, but it was just because they desperately needed servicing
Other than that, I can't think of any one specific amp where I changed my mind about it later. I'm very thorough with the way I test gear and do lots of AB comparisons with amps I already know well. I am very glad though that I later considered that I just didn't try the right version. I guess some say they're not a boogie guy or not a Marshall guy or not a Diezel guy, but I'm an everything guy with amps as long as the quality of sound is there, so that's why the right revision is crucial for me