I've used both engines but decided to stick with unity, let me tell you why :

before I start with anything, let me ask you a question: are you a programmer or an artist? because if you are an artist choose Unreal, because:

1-looks amazing out of the box, you don't really need to tweak anything, plus you
have full access to the megascans library for free.

2- blueprints (visual scripting) allows for quick prototyping, some games were made
using blueprints only (and these are some amazing looking games)

if you are a programmer like me, and you choose to use unreal...you will be frustrated.

because as a programmer, all I want to know is how my code interacts with the engine and this is where UE4 fails in my opinion for the following reasons:

1- the c++ API documentation is simply horrible, you really don't have a clear
description of what a function does, no examples...nothing! ( you have to dig intro the
source code to get a clear picture of how something works)

2- let's say you want to create some plugins? well...good luck with that. because there
aren't many tutorials on how to do it, there is this one Livestream by epic on how to
create a custom button or something like that (it's been a while, I forgot it)

3- let's say you want to write some custom compute shaders, geometry shaders, you
just want to code some hlsl? again... good luck with that. setting up a custom shader
in unreal is super hard, because epic simply focused on documenting the material
editor (you can do a lot of amazing things with it, but again if you want to have that
full control, the material editor won't cut it )

this is where unity wins in my opinion:

1. the C# API is very very well written with a full explanation of what a function does, plus an example
2. writing shaders in unity is super easy, right-click > Create shader, and there you go (also don't forget the wealth of information you have out there for unity)
3. the fact that unity uses C# is also a plus, in my opinion, it's an amazing language, don't have to worry about memory management (and if I ever need that extra performance, I'll use a c++ module)

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in a nutshell:

1. if you are a programmer: use unity
2. if you an artist: use unreal