If you discount <15wt practice amps, then I have another nomination:
Peavey Duel 212
Snapped it up secondhand for what I thought was a steal - thought I'd love it because it had all the features I wanted in an amp at the time. It may well have done except for one thing: TONE :( - the clean sounds were nice enough & the built in vibrato & reverb were really lush & full. But the lead channel was absolutely VILE - nasal, fuzzy, lifeless, muddy & any other negative adjective you care to think of :(
If playing my Miracle Man FV through the Recto with BBE is metal tonal heaven, then the same FV with a Duncan Custom (/spit) into the Duel 212 was the exact opposite :lol:
It was partly the speakers as it sounded slightly less awful when run through Vintage 30s, but still barely useable.
After a few weeks I relegated it to the garage & bought the Mesa Rectifier that I still use to this day... :)