Sram and Shimano are pretty much the same, although Sram cost more, don't last as long and are more fragile ime.
KMC chains last longer and run better btw
The clincher for me is cross compatibility, i've a few bikes and they all run Shimano, all the parts between the bikes work fine with each other. It all runs relatively maintenance free, is a piece of cake to setup, i can get spares for shimano in any shop, even
halfords 'shudders'
Sram x4 is about the same as Shimano Alivio, and Alivio is a league ahead in design, weight than the Sram equivalent.