What Engine to use for Level Design's

If you only want to level design, it might be easier to pick a game you like, and mod that game.

Some games still release with modding tools, like Fallout 4. For MP, CS:GO still has a very active and thriving mapping community.

Reason this is probably better for a beginner, rather than starting out with UE4 or Unity is that these games already come preloaded with loads of content you can play around and reverse engineer. As a beginner, it can be a little daunting to start out with an engine, since you pretty much need to do everything, even with all the marketplace stuff.

Understand how games are made, by reverse engineering them, then make your own.

I've been having a lot of fun doing level design for a game called Prodeus. The same level editor the devs use is baked into the game and it handles all the scripting/geometry/level distribution. Means one person can realistically make a level on their own without having to learn a whole bunch of different tools.

I hear godot engine is pretty cool

Don't bother using a tool that isn't for a game. You aren't going to learn anything if you don' have any mechanics with which to build for.

On top of what’s been already mentioned I’d mention Far Cry 5 and its arcade, which if I understood correctly back at the announcement, includes assets from FC3 and FC4 to use.

If you are into MOBA you can use Source 2 for Dota.

The latest Gears of War has a very easy tile-based editor you can play with (for that coop escape mode only?).

Trackmania used to have an editor, so check if is still the case if you like racing games.

If you want to learn UE4 I think Insurgency has an editor, I’m pretty sure they had a mapping competition.

Theres also a WW2 multiplayer game (UE4) that comes with an editor, can’t remember its name unfortunately.

I think it largely depends on your perspective of whether the world you are creating is additive in your designs or subtractive - and whether you would want to work in a modular design or not.

So, if you take a simple wall that needs a window - using something like the source engine would require a lot more vertices than the unreal engine, as the latter would require two cuboids and the former would require four.

Also, with a modular design, you are working with a set of pre-made polygons to suit your design - if all you have to work with is these polygons, you will have to kit-bash your way through a design...unless you build, model and texture your own polygons in blender/max/maya/modo w/e.

Perhaps the bigger question is what is it that actually interests you in level designing?

Unreal Engine 5 would be my recommendation to you, using subtractive geometry due to it's massive speed advantage.