What's "WYSIWYG"? D:
I used both the UEd and Worldcraft back then. I liked UEd better for all the features and what you can do w/ the editor/engine (in-editor preview, open maps, 3d skybox, rescaling models) but ended up using Worldcraft/Hammer more because I played more HL1 than Unreal games.
Another thing is that (Gold)Source is better for realistic games in my opinion and I like those better atm. Unreal has this "spongy" movement, if you know what I mean.
Then again, Red Orchestra is a great game but has some of this "spongy" movement.