Roping reins are usually better for a beginner. It can be a lot to ask a beginner to give the correct aids to a horse, navigate the trail and have split reins to handle on top of that. Things that are second nature to me such as adjusting my reins, can be difficult for a beginner.
A big thing to consider is the length of the reins when looking at roping reins. Many roping reins I see (I don't look at them much though, i'm a split rein girl) are on the shorter side. You need to make sure that when your horse is riding nice and relaxed with their head lower that you'll still have a slight drape in the rein. All too often I see beginners riding in roping reins because it's easier for them but they're constantly in their horses mouth because their reins aren't long enough.
As far as dropping split reins, it isn't a big thing to be worried about. Quality split reins will have some weight to them and length. If you drop them on your horses neck, it's pretty well going to stay put and not slide to the ground. Now cheap lightweight reins, yes they would slip. Short reins would also have a tenancy to slip.