Two different animals. The Smarty is a programmer, while the Comp is a power adder.
The Smarty is far better IMHO. It gives you the ability to read engine codes and reset them, allows you to adjust your speedo if running larger tires, cannot be traced by the dealer, has multiple settings from stock to snap your head, has a half power setting for emission testing (no smoke), built in high idle during cold weather and you can download upgrades (free) from their website.
The only negative to the Smarty is it can't be adjusted on the fly.
I've had both, the ONLY bomb on my truck that will never be for sale, Smarty!
The Smarty improves daily driving and performance incredibly. Your truck will build boost faster, so off the line it feels like a gasser! I did not get that kind of response from the Comp.
The Comp and Smarty stack well, but the best stack is a TST with the Smarty. That way you use the timing from the Smarty and get the fueling from the TST. By the way this is the recommended stack from Marco, the inventor of the Smarty.
No choice in my book. Have fun!