You didn't say what model but, i'll go out on a limb since the pic is a "HD/Duramax" and by the screen name 34 yours is too. 6" w/ 35's is the most common and imo the safest as dailey driver for the >3/4 tons. but in the 6-8" lifts the chebbies are running CST & RCD. I am looking for a smaller lift for the 1/2er, and both of those look good to me. Naturally they both have their own sales gimmicks and it boils down to what you like or how much you could save on it. both should clear 35's to 38" tires. Best thing is start looking around & going to the shops every once in while and see what others are running. I stop every time I see One and make note of likes and dislikes.
Sorry it's so long, good luck