I've been messing around with free profiles (from the online Rig Manager) with my Kemper and while there are some decent profiles there, I was never really convinced.
From the first time I tried Kemper, I instantly loved the "TAF \m/ Van Halen" profile and I still do, and no other profiles have really had "it" like that one... But I wanted to try some more and finally decided to buy a commercial profile pack.
And what better place to look for than The Amp Factory and their 5150 profiles? Hehehe! Downloaded and while I initially thought "well, it's good" it wasn't until I started tweaking with the settings it really shines... EXCELLENT thrash metal sound. String definition from hell!!!
It's the first time buying a Kemper profile pack and I might do it again, seems like it's totally worth it.
Here I play some random thrash riff with my Fender Musicmaster loaded with an EMG 60 in the bridge.
There's some great commercial stuff out there and a lot of shit, but if you find the right guys then they are way better than what you will find on Rig Manager (understandably). The stuff that's worked for me so far has been:
Lasse Lammert Profiles - I'd say his pack you can download from Kemper is the best free stuff you will find.
Stymphalian Productions - James is an absolute tone master, his Recto pack is phenomenal and he's got some great bass tones. Sometimes his cab/micing technique makes things a little to prominent in the top end around 6 & 9khz, but you can either swap cabs or EQ to work on that.
Sonic Underground - Their Ampeg SVT Classic Bluelines pack is a must have for bass tones.
Till Schleicher - Till is the king for heavy guitar, his Chimera and Cab Lab packs are absolutely must haves. Everything that I and my other guitarist use features Till's profiles, they are that good.