The SRAM is pretty stiff because of the external bearing GXP bottom bracket. You could get the SRAM S100 but that has a power spline BB like the Truvativ Touro. I have a friend who uses the SRAM S300 and he likes it a lot. Its maybe second or third to the more expensive Omnium but I'm pretty sure you wont find a better bang for the buck.
yes they're entirely different cranks. the 300 is redesigned and much nicer.
i have a truvativ elita compact crankset on my road bike and the crank bolt kept coming out. they fixed it on the newer bb30 sets but i'd get the 300 and NOT the 100. for the s100's price, i'd get pake or iro or 1/8 inch or origin 8. they're all pretty similar and they'll all be easier to install. you have to really torque the **** out of S100/S300 crankbolts.