We chose Sungain Solar because they offered REC panels with a 25 year guarantee and a Goodwe inverter, which seemed a good choice. They offered this at what was marginally the lowest price, and they also gave us a lesser option. The main negative of the company was that it did not yet seem to have a strong track record, but we appreciated the fact that offered a 17-year guarantee on installation. Of the other quotes we received, one only slightly higher was from a well established firm that offered panels that did not seem quite as good, and one that was higher still offered what seem to be excellent panels (Seraphim) but an inverter that seemed no better, coupled with software that seemed difficult to use, and the company had somewhat mixed reviews with regard to customer service.
The installation went smoothly, with no issues at all, and the company handled all required paperwork to put us on the grid. We have not yet found any reason for complaint, and hope none well arise, though of course this makes it impossible to judge post-sale customer service. Overall we see no reason not to recommend Sungain Solar to others.