Guitar Rig 5 is the ultimate guitar effects VST / amp simulator I've ever used. With an easy-to-navigate interface and a plethora of diverse sounds, Guitar Rig 5 is a formidable beast in any guitarists arsenal. Not to mention the customization capabilities are both fun and educational.
Guitar Rig 5 works exceptionally well in my DAW. In applying additional FX to Guitar Rig, I experience no CPU spikes, just a killer tone I'm grateful to have at such a low price. Not trying to make this a sales pitch or anything, I've just used this program extensively for several albums, and hundreds of songs by now, I imagine. I use it exclusively for solo guitar recordings.
The best part about Guitar Rig 5 is the ease of use. This is the best alternative I've found to recording microphone-to-amplifier. That process can be tedious, and microphones are expensive - this I can plug right into my audio interface and get the sound and levels I want with way less of a hassle. I highly recommend Guitar Rig 5.