When it was UDK VS U4, U4 was faster and easier (although hated that old buggy monodev! still do). I just didn’t like UE script much and found the construction tools naf and buggy in UDK. Still not a great fan of the UE4 flight controls (but I am a Max-er not a Maya-er, so always hitting the wrong keys and zooming off into space! - I wish there was a switch to use Max flight controls!!!).
Prototyping now can all be done in BP - and some of it left there too - rest converted to C++ for speed later, when happy. Now that it is free, almost completely reloadable from the IDE (not so often having to close the IDE recompile and reopen etc), Unity has to be watching its back ($75 /mo is high now - and the free version is still lacking in very basic stuff like shadows). AAA’s are unlikely to chose Unity over the other Engines (or their own in-house), so it is Indies and small devs - and thy are being chased away by the cost and attractiveness of UE.