I have a Trek hybrid and a Fuji road bike. The hybrid has riser bars--basically flat--and I have frequent episodes of hand numbness when I ride it for any distance. Hand numbness when I ride the road bike is rare. Drop bars give you many positions for your hands, and I find riding on the hoods or just behind the hood is a comfortable position.

I suppose the hand numbness on the Trek could be relieved if I brought the handlebars up some, but then I'd be much less comfortable on the saddle.