You certainly should play them both and compare before you buy.
I have TDW-20 with TMC-6 which allow me to add up 5 tom-toms and up to 10 cymbals and few bass pedals and I know that premium models of Roland much better than Yamaha in all aspects: quality of drumheads (quite mesh pads v. rubber pads), modules and their functions etc.
However I have tried Roland TD-9 and it sounds better than Yamaha, because it's a budget model it doesn't mean that they have cheap synthetic sound, even Roland HD-1 model with limited number of pre-sets has a better sound than Yamaha equivalent.
Recently I tried the newest flagship Yamaha model: no comparison to TDW-20 whatsoever. Therefore personally I prefer Roland, market leader in e-drum gears.