40-55 is great for questing, imo :P

in any case... when I was doing RaF I did 1-10 by hand, 10-20 in sfk, 20-40 in sm, 40-55 in BRD, and 55-60 in Ramps.

However, if you're a multiboxer and only doing 2 accounts... 40-55 would be best spent in feralas, hinterlands, and felwood.

[edit]: and to the contrary... 20-40 are the worst levels imo because the zones just suck... when you get past 58 you get to experience really fun questing areas... it has nothing to do with monotony... it has everything to do with quality.