I just sold a 300C SRT8, and got a bone stock, low-mile QC SRT-10. As others have said, the SRT8 is faster than a QC.
With the "restructuring" of my garage, I just needed a 4-door truck more than a 4-door car.
Both vehicles can be modded. There are plenty of SRT8s running high-12s with nothing but a flash and an airbox... probably about like a RC with the same mods.
What it will come down to is what you need and prefer. While I have no experience with an RC, I am sure it is on par (or superior) in handling to a Lightning truck, and my Lightning truck will outhandle my SRT8. If you want exclusivity (not a big thing to me, but is to some and it certainly helps resale) then a RC SRT-10 is lightyears ahead of an SRT8 (300C, Charger or Jeep). If you want to row gears, you only have one choice. If you want a truck bed to put things in, you only have one choice. I'd also bet that mod-for-mod, the SRT-10 will show more gains, although my experience is limited thus far. It's just an educated guess.
I liked my 300C SRT8. It is a nice vehicle, offers some decent refinement, drove well, and gave me no problems. I'm just more of a hot-rodder, so I'm opening up some space in the garage, along with adding an SRT-10 QC.