UnrealEd is way more powerful than Radiant. At least there's one feature that kicks Radiant's ass all over the place: you can practically model the whole map in 3dsmax, XSI Mod Tool o Maya PLE and import it into a level space.
Other features that makes UnrealEd better than Radiant:
- You don't need to spend an hour compiling to preview how your map is really looking (the editor is wysiwyg)
- You can import, compress and make your shader file right in the editor (no need for lame MFC shader editors or text editing)
- You can import static meshes from your favorite 3d suite and use them not only as props, but also a level geometry (and the triangle throughput of the unreal engine is extremely fast).
- You practically can manage every asset of you mod or even the original game's from UnrealEd.
- Epic has released an amazing IDE specically developed for UnrealScript, which give programmers all the power and flexibility they need to code their mods.
Rounding up, I cannot enumerate all the advantages of the Unreal Engine over any version of the Quake 3 Engine since they are too many. But the most important thing is that unreal editing is extensively well documented by the developers themselves, so you don't have to figure eveything out like we had to do with JO or JA.