There's nothing wrong with the old school design, so long as you only intend to shoot with the iron sights already on the gun, or if you're doing one of the retro builds.
However, the old-school carry handle becomes a massive hindrance when you start looking at using optics on the gun. Flat top guns have the widest array of available options, and it's much, much easier to install a scope on them. All you have to do is slap a Picatinny-compatible scope mount on and you're ready to go.
The number of mounts available for putting a scope on the carry handle are quite limited, and in my opinion, generally look and feel much less solid than a decent Picatinny mount from an outfit like LaRue. They also make it much harder to get a decent cheek weld for the average shooter, since the scope ends up being so much higher than the bore axis of the gun.
Again, while there's nothing out-and-out wrong with a traditional non-removable carry handle, choosing a rifle in that configuration does end up limiting your options for modification down the road.
Based on that, I generally recommend going with a flat-top design.