Only Red has zero loss on the rear. Force has it on the front. Zero loss is a feature I wish I had. in that light i would recommend spending the extra for the Red shifters if the extr spend is not an issue for you financially.

That said i have raced on Rival shifters for 2 seasons and i haven't missed a beat.

Functionally all groups are the same. they all have gears and they shift. The only group with a functional difference IMHO would be Shimano's Di2. So....pointless to discuss.

Red overall has many differences - the chainrings are a different material, the crank is different, the RD has a full carbon cage - Force is 1 plate carbon, RD has ceramic bearings in the pulleys (yay....), BB - most off the Shel Red groups would be spec'd with the Black box BB which is ceramic, Cassette - 1090 single piece over the Rival Force 1070. I won't discuss the chains because all of their 10spd chains suck IMHO.