Great sounds
I'm uninterested in the "does it sound real" conversation. My concern is that it sound good.
I like a heavy, distorted sound; Smashing Pumpkins, My Bloody Valentine, Alice in Chains.
I have GTR3. My first emulation program. Has worked well for me. Mind you, the final sound I get is after using eq, compression, fx, etc.
I got the s-gear demo. The Marshall head sounds great. The clean sounds were not very useful to me. Can't justify $99 for that one sound. Maybe later.
I'm impressed with Amplitube emulations. The Orange and Ampeg stuff is beautiful.
I'm also impressed with their business model. You can buy emulations and effects a la carte. The program itself is free and comes with some good emulations.
Charging hundreds of dollars for software bundles often leads to piracy. Some people can't afford it and others don't want to spend a lot of money for one particular effect or emulation.
Its the pricing scheme of the future IMHO. It's like TV. I shut off my cable because I was paying over $100 when there's only like four or five shows I like on TV.
But I digress.
I'm more than happy to pay for my Amplitube stuff because I can buy the specific piece of gear that works for me.
I tried Overloud as well. They have good sounds but like most people, I found the interface annoying. You can figure it out if you invest a little time.
The softube emulations are good as well if narrow in application IMHO.
If your budget is limited I would dive in with Amplitube. It will get you started.
Waves GTR3 is $120 from audiodeluxe.com. Totally worth the money. Great emulations and great fx.
NI guitar rig is a good program too. I demoed it and it sounds great but i couldn't justify $199 seeing as I already had GTR3. They do have a stripped down version for free. If you like their sound you can always buy the full version. Or not. There's enough in the free version to make music.
Like guitarists who use physical gear I shape my sound with products from different manufacturers.
Basically all the major programs are more than usable. Whether or not you get an "amazing" sound is up to your creative and engineering skills.