I've used DT Register on about a half dozen commercial sites, and I'm convinced that I made a good decision in going with it.
* Very comprehensive
* Easily customizable
* Numerous payment options, including PayPal Pro!
* Handles complex fee considerations
* Nathan provides very good support
* While it's not exactly cheap ($75), it's a LOT of component for the money, especially for a component that you're trusting for ecommerce.
* YouTube training videos.
* There's a significant learning curve for this component.
* While version 2.7.9 is stable, earlier versions of 2.7.x had enough bugs to be problematic. Make sure you check the vendor's site regularly for upgrades.
Overall, if you have events that require complex registration forms, DT Register is the only way to go.