are you asking about being an admin on servers for these - the DBA - or are you asking how they are to actually use?
to use they are retardedly easy - esp the MS stuff - it just takes time sitting in front of it.
Oracle is easy in some respects, but more complicated than the MS, but that would make sense since it is better.
also you have to have some knowledge of a unix system which people coming from windows sometimes see as a hurdle and added complexity.
as far as creating tables, databases, querying them, reports, etc - they are all easy.
creating something useful that actually uses them - that is entirely different, but hardly the role of the DBA.
and Oracle DBA with experience makes what is known in the industry as "a buttload of money" and they do soley that.
MS SQL DBAs are usually people that know other MS stuff and can serve as more of an IT person - at least this is how I see things at the various places I have been.