There are some really good questing zones out there for basically every expansion, you just need to find them haha. Silverpine Forest f.e. will forever be my most beloved leveling zone, all my chars went through it, and it never gets stale. Tbf it seems like they had the perfect formula there but never used it for other zones. You have lots of frequent rares which give quite a good junk of XP, a great story, you ride alongside Sylvanas, it has an awesome ending and I think the first ingame cutscenes (the lower quality ones with your character) they ever did. Just get yourself an artifact weapon at level 10 because they are quite OP at the start. Sprinkle a few dungeons in it, get your Garrison for your free lvl 25 pet later on and you should be 50 at the end of your favourite zone(s).
Btw, from 50-60 you can now do a daily Torghast run which gives 30-50% of a level and is surprisingly fun.