I'm one of very few on the forum that have run both on the same chimney during the same heating season. So to me there is no comparison. My smaller Crawford 20 burned less coal and provided the same heat output. By that I mean the C20 kept the house at the same inside temp as my larger (firepot size) Harmon MK II on the same outside temp days. The style of antique I run is also much less dirty to service. Once you run a base heater with an internal check and ash pan that is larger than the grate area this becomes evident.
New stoves certainly get the job done, just not quite as well overall as the high end antiques. As Oliver says, I'm sure there are poorly executed early stoves.
For me, it boils down to this
I can't stand looking at a black box in my family room.
Some guys can't stand looking at a black cylinder dressed up with nickel in their family room.
Different strokes for different folks.