Switching over to UDK or Cryengine would mean starting from scratch again.
Level creation is so much different from source and it's not enough to be a mapper anymore, you'll also need to be able to produce your own models.
Roughly 90% of a UE3 map consist of models with only a tiny bit of brushwork involved, while in source it's vice verse.
Also UDK is much more complex and complicated. Allmost every feature you can think of and even some you'd never think of are in there and every single one has dozends of parameters and values to toy arround with.
The issue with this is to find the ones you need within all these expandable menues.
In terms of mapping i really prefer Source's Hammer, nice, clean, well structured and easy to use.
While it takes a little effort to learn mapping with Hammer, it would take a seriouse ammount of knowledge in several fields to produce a map for UDK if you're not only planning to stick together some default assets.
As for CE3 i cannot say much beside having played crysis, read the feature list of the CE3 SDK and toyed arround with the FarCry1 editor a little.
But so far the toolset should be more or less equal to the UDK, feature wise.
As for source, it's far behind with the toolsets and features now but still a good engine.
I'm sure with a huge toolset and engine update they could be up-to-par with the other engines again.
On the other hand, if you create a beautifull map with UDK it's just a good looking map powered by a potent engine, but if you create a map on source that is far better then everything you'd ever imagined comming out of source....
....just look at Dear Esther ...or maps created by the GES team