I am a happy S-Gear user but I just ran across this free Amp Sim and was very impressed. This is now my "go to" recommendation for free/inexpensive Amp Sim plugs.
https://tonelib.net/gfx-overview/
(This was discussed over in the Linux forum, but I did not see it mentioned anywhere else. I also posted this on another "Free Plugins" Thread, but this thread looks more comprehensive.)