Obviously the two have different looks to them and the red dot is less chunky so you can see more of the area at once.
But is there any differences to them other than that? Do they affect the weapons stats?
Difference between the red dot and holographic sight
playerunknowns-battlegrounds
Related Solutions
According to this forum post the:
Vertical does horz/vert recoil in a larger percentage then the angled but the angled lets you ADS faster while still giving small vert/horizontal recoil reduction.
This information seems to have come from one of the dev streams(Twitch link seems to be dead) and looks to be confirmed by additional forum members. Not sure how exactly accurate it is though.
There may just be coincidences with a lot of people having similar gear. I often see the same stuff because people aim to get the better gear and obviously level 3 gear will be the most benefit to you. The places with higher loot spawns, and better gear tend to have a high percentage of players dropping at so it's not unlikely you'll see a lot of players with that better gear.
As far as I known in my time playing, and from reading forums and threads about loot spawning, there doesn't seem to be any particular weight applied to certain things spawning in different matches.
Common loadouts are ARs with a shotgun or SMG, in my experience, which is why they're so commonly seen. The more powerful guns have less frequency so that also contributes to seeing more SMGs around the place.
Some early threads like these all mention how it's weighted towards certain zones having better loot, and the farther away you are from them, the more RNG is factoring in. In my experience the more isolated places tend to have some things in them, and a variety of gear, but there is the chance nothing/little amounts of things are there.
If you check out various loot spawn guides like this or this, they'll tell you that you're guaranteed better things at places like the Military Base, the School, or the Power Plant to name a few.
Here is an image which shows the general distribution, and as you can see, some places are much more weighted in the amount/quality of loot spawned. 
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Best Answer
There is no statistical improvement by any of the scopes, they just give you further zeroing distance and allow you to shoot enemies at a further range with (relative) ease.
The only differences between RDS and HS is as you mentioned, the size and shape of the physical sight as well as the reticle, and according to this source, the holographic zooms ever so slightly farther.