Not allowed to use them where I hunt, but I would go with a doe. The only reason I say that is because to see a doe in the field in early season gives a sense of security and safety. Has the season goes on you can use the doe during the rut. Just my though process. Maybe someone that uses them will have real world experience.
I use a buck decoy. It has not helped me take any large bucks, but it has been a lot of fun during the rut. Reason being is watching bucks come in and check the decoy out. First buck that ever came in to the decoy knocked the buck off the stand and broke the steel stand. I was shocked at the power this buck hit the decoy. I have used it for several years now, Every year, during the rut, its a lot of entertainment. It was worth the price.
I used one the first time 3 years ago. It made lots of difference. The first evening I called up a large buck with a rattle and grunt to 30 yards then nailed him with my crossbow arrow.
Several other times thru the season I used it to bring bucks up. I did one for my son but he messed up and didn't clean his ML so it walked away. Other times the bucks were smaller than I wanted but it a plus to have one. I had the Big Boss buck decoy but I always figure one could leave the angles off and it it look like a doe decoy.