If you are only running TMCC locomotives, then get the Cab-1L. If you have Legacy locomotives and a Legacy base, get the 993 set, otherwise get the 990 set if you need a base too.
I have my old TMCC base connected to my Legacy base so I can use the Cab-1 to run TMCC locomotives. In my head they run better that way. My Cab-2 took a dump, so I found a good deal on a 993 and bought that so that I'd still have a Cab-2 when I send mine in for repair. I tried running my Legacy locomotives with the Cab-1 until the 993 get in, and it just wasn't the same, I missed too many things you can only do with the Cab-2.