I have been using DTregister for going on 2.5 years. It is by far the best events component available at this time.
Support has been excellent - only a couple of glitches in all this time. This last one is a strange glitch, but Nathan got everything working again.
As far as the component itself it is very full featured with everything you would want with event registration including many payment gateways, ability to offer events free, e-mail handling, integration with several other components including jomsocial. I really like it because it is so very flexible - you can set things up various ways to meet your site and aesthetics needs.
I heard that it's going to get even better soon.
I thank them for continuing to support Joomla 1.5 as some of us have such large sites with so many extensions that upgrading has to wait until a better time of year to upgrade.
Thanks so much for creating and continuing to improve a fantastic component!