Most electric guitar VSTi provides the built-in amp sim these days. However, I found the sound quality is not as good as other amp sims such as Amplitube, Bias, Guitar Rig, TH3 to my ears except Shreddage and Orange Tree Evolution.
What do your ears say?

 

Last edited: Dec 24, 2020

Ample Sound ampsims included in the v3 line sound quite well to me. And light on CPU.
This is inevitably biased, but when I played Rammstein Du Hast riff preset I almost had a boner.

 

Stuff in Kontakt uses Guitar rig amps, so if you think Guitar Rig sounds better, buy new ears...

 

The only amp sim that made me stop leeching on the OTS Evolution Rock Standard built-in amps is S-Gear. And even with that, i still come back OTS. Go figure.

 

You could try to buy a small amp and microphones like a Shure SM87 and capture that. Buy used and sell the kit if you don't like the setup and not loose any money on it...then play yur gitar 8 hours a day to sound like this guy. I bought this Vox AC4TV for 100 bucks.

The little amp is killer and I paid 100 bucks.

I also bought a Strymon Iridium for when I cannot make any noise and for the flexability to use any 96K impulse responses available. I usually buy gear used but hit this when it was first released and am happy as a clam. I haven't seen one come up for resale, ever. That's lots of happy campers out there. It reacts to me as close to a real amp and speakers as anything I've ever tried for lots more money.

 

Last edited: Dec 25, 2020

I personally prefer to have more control and hence go for external amp sims. Personally, that leads me to better results.
However, I agree with @Xupito on his comment about Ample Sound in-built amps, they are quite good.

 

I don't think the amp models in Kontakt have been updated to have the latest GR has to offer, so there's that.