Calvin is being introduced to the wonderful world of competing command systems. 
There are many threads that come and go here about the pros and cons of the two.
As far as operation, either DCS or Legacy will give you a complete operating environment with control for locomotives, accessories, switches, etc. It really comes down to which manufacturer makes products that you'd most like to own. In my case, I had TMCC, then Legacy, but MTH kept making some neat stuff as well, so I got the DCS system. This allows me to buy any O-gauge command locomotive and have full functionality with them.
I'd recommend you look around for a train club near you, many of the members will welcome you to their layouts, not to mention if they have a club layout. You can get your feet wet with both systems and also discuss what products are available from each manufacturer.
