My only experience is with a Vortex Venom mounted on a XDM. Fantastic sight. My AR will be next and it will be Vortex, probably their holographic sight.

The Vortex Strikefire II is a very good red dot sight and comes with the Vortex VIP warranty for $179 and sometimes they will ship with a free mount. I'm a competitive shooter and I've ran this sight hard and it hasn't ever failed me.

Vortex SPARC AR. Love this optic. zeroed it in at 100yds and have been smoking ground squirrels with my AR first shot at 35+ yds

Holosun - 30.000 to 50.000 hr battery, optional Solar panel backup, Dot or circle dot reticle option. As good as Aimpoint for half the price.
I bought the HS515CU model and love it...

Love my vortex spark Ars...ended up getting two of them after the first. For the money can't be beat.

Trijicon MRO

Bushnel. They are cheep and work great!

I have been using a Burris Fastfire III 8 MOA for over 2 years now in USPSA Carry Optic competitions (sight is mounted on handgun slide).
Over 10000 rounds later and just one battery change this optic is definitely a champion.
It took me only 5 rounds to sight it at 25 yrs and I have not touched it since.
I compete against several other optic brands and even with the most expensive ones many have had to send them back and replace it.
Based on my use and by the cost there is definitely no better optic outthere.
Hope this helps

For price point I think vortex is the way to go. I am a big fan of the Sparc II and have used the spitfire as well. Vortex has terrific customer service as well.

For a home/personal defense rifle, the Aimpoint PRO is hard to beat. I lprefer the dual-illminated Trijicon RMR but they cost more.
For a range toy, the Primary Arms MD-AD is a good value.

The recommendation so far have been good ones: Vortex, Primary Arms, etc. I would also add the HoloSun red dots. If you are looking for something VERY affordable take a look at the TruGlo red dots. They are inexpensive, but the one I have on my "beater Ar" is holding up just fine !

Vortex striker fire II, great quality and can't beat the quality. I have 2 and haven't had one issue.

For a Weaver mount, I recommend the UltraDot L/T - have 2 on my SW M41 and Ruger 10/22 and they work great. ~$230
For a Picatinney mount, the Vortex Venom - have one on my XDM Comp .45 - great ~$220

Vortex Strikefire II has been my go to for a decently priced red dot. Or if you're looking for a little bit of magnification then I'd say the Spitfire 3x prism by Vortex is nice as well

Vortex Strikefire ll. Red and Green dot. Great optic. < 200.00