Best (guitar) amplifier plugins you can get. Period. Well..imho.
So let's get a thing out of the way right at the start: I am a "form follows function"-guy so I don't care about how it looks as long as all the information is easy to access and the handling is just as easy. Thermionik fits that bill. This is provocative but: if you have to have some high resolution fake-amp GUI in front of you and can't trust your ears alone then you shouldn't trust your own ears at all. The only drawback from Thermionik's ultra-simplistic GUI is running several instances of similarly featured amp models. Guaranteed to touch the wrong dials sooner or later. But that's what ctrl-z is for...
I've owned PODs, Vettas, Blackstar ID TVP...whatever, VOX boards, Korg boards, DigiTech stuff, TC electronic, BIAS plug (thanks focusrite), Amplion, of course LePou and Ignite Amps and more, tried intensively whatever I could (software and hardware) and that's just the digital stuff. I never was quite happy until I used Thermionik (5). It just sounds right. Of course: to my ears. It's extremely easy for me to dial in the sounds I want no matter if clean, glassy crunch, heavy crunch or metal is needed. That results in a very streamlined workflow for me without which I would never have released the 28+ songs I stitched together over the course of the last two and a half years. I've spent hours on end trying to achieve sounds I want before Thermionik. Now it's simply "I want this and that", dial it in - go. Yet it's still so much fun experimenting with the amps and just play. Especially if you keep in mind that the "Input"-knob on page 2 is extremely important. Want to play Death Metal (or Doom..) with the Chimp (Fender 62 Champ)? There's enough gain in there. Thermionik is not just a simulation of what's there but also a lot of what's beyond that (the developer himself stated that). It's fantastic and gives you a lot to play with. Of course that means that if your interface and/or guitar gives you quite a hot signal that it can be better to reduce the Input quite a bit to improve the handling of the gain knob.
It would definitely be quite too much to describe all the amps in detail here but if you want to check it out (and you actually can go and try it out fairly easy!) and need some hints at what to load up first: the two Vocal30s (compare them...all the AC30ness you'll ever need), FB100 - workhorse for absolutely anything you throw at it, Jump79S - a '79 JMP modded by Soldano...it's glorious and if you want metal: try the Serpent, if you want something really quirky give the Super 1690 a try. Of course you ideally use Recabinet as your IR loader behind Thermionik and use really good IRs (I personally love the valhallir IRs) - well at least make sure you don't use some ten year old stuff that isn't quite up to the task in 2018.
All of that is still just my opinion and to you it might be more important how it looks or you just think the handling of single plugins is too cumbersome and maybe it just doesn't click with your ears. To me this is it. No more searching, just playing, recording and enjoying it. And I strongly suggest that you at least try it out.
I tried many, many guitar amp simulations - everything from the very first POD generation to PODxt, Guitar Rig, AmpKit, Bias, ReValver, TSE X50 etc.
Never tried a Kemper and/or AxeFX though as they are just too expensive for me so I can't compare Thermionik to them.
For my purposes (mostly high gain guitars) Thermionik gives me the by far best results and feeling. The Duality (Dual Rectifier) and Psycho B (Peavey 5150 II) models are just great and for clean guitars the Vocal 30 (Vox 30) model is very easy to dial in (just 2 knobs - love it!).