I've got an el-cheapo Chinese reflex sight (it is sold under many different names - mine is "Tru-Glo" brand):

https://www.amazon.com/Ohuhu-Green-Sight-Reflex-Reticles/dp/B06XH22W2D

The above webpage shows the reticles but the below photo is from the package mine came in and has the reticle sizes:

https://i.imgur.com/JmXr79V.jpg
Edited: very large image edited to a link.

I prefer to use the 5 MOA dot since it doesn't obscure other parts of the target - the game is generally a similar colour to the background so it helps me to see as much of it as possible.

I tend to use red more than green. I though green might be better in bright light but not so sure about that. The sight has 5 intensity settings for each of red and green.

Also note that sideways parallax is good but vertical parallax is horrendous on this unit - it has a "rear sight" built into the rear housing to aim with and that places the dot towards the middle of the lens. If the dot goes above middle the parallax gets exponentially worse. I think that is why it is so cheap, but okay providing you are aware of it and aim properly.