Consider where you are going to be riding it. If it's going to be ridden off the paved roads and well packed gravel where you might struggle to steer, then you might go for a wide flat bar. Though I'd look for something with the ends angled back at me. Maybe a real wide mustache bar.
But if you are going to be on paved or well packed gravel, then IMO, few things beat a decent drop bar that isn't any wider than the acromion where your clavicle attaches. For longer riding times one might do on a road bike, I've found wider bars undesirable as they brace you too much and your arms and shoulders get all of the road swaying road forces that the body could share some of. But as usual YMMV!