This is my first hand experience. I have a 40mtr dipole at 50 ft and a 40 mtr 1/4 wave monoband vertical ground mounted and 60 radials. After 3 years of this arrangement I can truthfully say that the vertical is by far the better antenna for DX and most of the time it is better for Domestic.
I ran long term comparisons between a dipole (broadside) at 45' and a 40 meter vertical with an excellent radial system. DX was generally a toss-up; stateside, the dipole was better. Pretty much what others have suggested.
I tend to use verticals just because my dipoles--while they can work very well if up >50'-- keep falling down.