The first question is Glass or Dot? With glass you will get more precision. If you are looking to make accurate shots go glass. When you decide to go glass, go as nice (expensive) as you can afford. You will not be disappointed. A lower power (2-7X) may be a good idea.
With dot, you get faster target aquisition. Holo sights and tube dots have slightly different characteristics. EOTech and C-More are two of the top brands of holo sights. EOTech "looks" more rugged and has many options, especially for batteries. You can get a AA version or a CR123 version. The circle/crosshair/dot reticle of the EOTech is very fast. C-More has different sized dot modules you can choose from and change out if you wish. The C-More "looks" more fragile but I have had the scout scope for about 8 years and it is holding up great! The C-More uses a tiny little battery but I have only had to change mine once in 8 years.
Aimpoint is the premier tube sight. As stated before, the Aimpoint is the top tube sight. It also has the versatility of adding a magnifier.
If cost is a major concern, I have had pretty good results with the BSA holo sights and tube sights. They use disc batteries that are pretty easy to find but don't last as long as the others (but still have pretty reasonable life). BSA makes two different Holo sights. One has 4 different reticles and one has four different size dots. The multi reticle version is pretty cool for under $50.