Septicdeath, it depends on what you want to do. UltraDot is a red dot of choice for a lot of NRA Bullseye shooters. You can get it in different size tubes and even with adjustable MOA dot sizes. Best of all, it is made in Japan and not China. I have 4 or 5 of them in different iterations.
If you are looking for something more field friendly, check out the Aimpoint Micro T2. Wicked good and wicked expensive. I have one mounted on an AR 15 with a quick detach mount from LaRue. In my opinion, the best you can get.
Also field friendly are the Eotech holographic sights. I have one of these on an AR 15, but like the Aimpoint better.
None of these are cheap, but would work well on an air rifle if you do not need magnification.
Mike