This is a tough one...
Personally, the MTH ProtoSound 3 system has a better sound/control system in comparison to LC and LC+. Looking at the detail and appearance of the sets, I'm partial to MTH. That being said, Lionel's LC and LC+ system have a very "fun" remote and it is very easy for all ages to use. I think MTH would be the better option since I have been running R-T-R engines that I have had for 17+ years and the only work I needed to do was replace the batteries (or install a BCR). Are you thinking of a freight or passenger train set?