The eTap theory is that smaller chainrings and cassette cogs require less energy to spin, thus maximizing the effects of the two watt-bombs extending from the rider’s hips to the bike’s pedals. Smaller is lighter, lighter is faster, faster is better, better is on the podium. Overall, the gear ratios are very similar between the two choices, but the 12 speed cassette offers smaller steps to really fine-tune your cadence. I’d go with the SRAM option if I could. No problem with Shimano’s two top tiers here, but I think the eTap might just b3 the coolest thing in a while. Plenty of pro teams are riding SRAM, too.