I definitely recommend these guys for solar panel installations. For the installation at my house in the early fall of 2014, I've queried and compared several contractors, including the nationally known installers. (I think I generally compare at least 3 ~ 5, if not more, contractors before hiring one.)
Bottom line is that not only did 21st Century provide better deal and better hardware, but after conducting some due diligence, I believe these guys were most trustworthy. Unlike the other installers (including some that had very good rating on other forums such as Angie's list), I felt that these guys weren't out to just make some quick buck. For instance, other installers will do anything if it means you are spending more money. At least one of the other contractors even made promises which I actually knew they wouldn't be able to deliver on. Also, all the other contractors "recommended" certain equipment based on their "opinion." But in those instances, I learned that their "opinion" = "$ interest" because those installers were also equipment sales guys ... so if I used their "recommended" equipment, they made money on not just the labor on installation, but also on the equipment. However, it was clear that 21st Century had no such conflict of interest. They would install pretty much anything I bought ... except that they'd provide me their opinion. In one instance, Rob at 21st Century actually made me think twice about a set up that would've been less cost effective for me even though it would've meant more $$ for 21st Century.
Having actually hired and worked with several contractors on a few big projects before, I knew that it's a rare thing ... a contractor who cares about the customers' best interest. Also, I appreciated their flexibility and promptness. The installation guys seemed like a nice crew.
Again, highly recommended. I'd give them 5++ stars.