Which is better, the iPhone SE, iPhone XR, or OnePlus 8?

I will divide this answer in different parts -

Part 1

Talking about Performance -

The Best one is iPhone SE

Then iPhone XR and OnePlus 8.

In daily usage, all of them performs excellent.

You can choose any of them.

Part 2

Talking about Software Updates -

Both iPhones are better than OnePlus 8.

Part 3

Form Factor -

Oneplus 8 is a huge Phone. It depends on you if you prefer bigger screens. iPhone XR comes in the middle neither too big nor too small. iPhone SE is the smallest one ( 4.7 inch ).

My Pick would be iPhone XR

Part 4

Screen / Display Quality -

OnePlus 8 is the best when it comes to display quality. iPhone XR comes in the middle. In daily usage, you won't feel any issue with iPhone XR display. If you are comfortable with small screen size, then iPhone SE should be your pick.

Part 5

Camera -

Best Video Quality -

( Great to Good when compared with each other )

1. iPhone SE
2. iPhone XR
3. OnePlus 8

In daily usage, iPhone's video quality is better.

Capturing the Portrait shot -

1. iPhone SE
2. iPhone XR or OnePlus 8 ( Almost Same )

iPhone SE has lighting effects which OnePlus 8 doesn't have the same.

If you are a noob, then all of them are best.

Part 6

Battery and Charging Performance -

OnePlus 8 is the best pick when it comes to charging speeds and Battery performance.

You should buy seperate fast chargers for iPhones.

Conclusion -

1. If you don't have any issue with iOS, small screen size, then go for iPhone SE.
2. If you want Bigger screen and iOS, then go for iPhone XR.
3. If you want a flagship android phone in which you can customize almost everything, then go for OnePlus 8.

All of them are almost same in daily usage.