Best thing to do is try several different kinds out, if you can. I say this because what works for one person may not work for you very well and vise versa. I've used EOTechs for years and finally did the ar15.com mantra and "bought both". I used the Aimpoint M2 once at the range. It's now being traded for another EOTech.
Three excellent sights to look at are the Aimpoint, EOTech, and Tripower. Each are very high quality, and each have their own merits. The only way to know what will satisfy you is to experiment.
As far as price, the EOTech definately wins because you can get new ones (depending on the model) for around $300. Sometimes they pop up on the EE for less. The Aimpoints and Tripowers require a mount, and a good mount will run you in the realm of $100 +/- a little. Once you narrow your search a little, just contact one of the vendors on this board. They usually have some of the most competetive prices and are very helpful in getting you set up with what you need.