multisport

I am in the planning process of converting a 2002 hybrid to a cyclocross bike. I think I will be sticking with the non-drop handlebars at least for the time being since I won't have to replace shifters and break levers. When not using drops, is there a general preference regarding flat bars vs. riser bars? My current bar is a riser 24.5" long, with a 50mm rise x 15 deg. I think it is a bit too much rise--especially with an adjustable stem. I've heard that flat bars can make one hunched over a bit too much, but would that be mitigated with an adjustable stem? Would a riser bar be better?

Thanks.