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.
That's the real issue as far as I'm concerned. Especially if you're opting for a diesel set, flat handrails are a deal breaker for me so no LC+ diesel for me. However, I really dislike the DCS Explorer and using my phone as a remote. It's a tough call.