Which is best?

Rival

Why?

Depends if you get on with Double Tap or not.
I don’t.

Had tiagra liked it now have force like it more.
Purely down to preference id have tiagra over rival as to me it feels better.

Have switched from 105 to Rival just today in fact. So far so good, took me all of 30 seconds to get used to DoubleTap on my first ride today. I like it anyway…

Apex is more Tiagra level. Probably syill slightly above. Sram groupsets are generally half a level above Shimano ie rival is between 105 and ultegra

Rival will be lighter by a fair bit.
And for me is a cut above Tiagra.
Also Shimano isn’t exactly known for lightness.
I like the precise and solid action of Shimano.
But Tiagra – the hoods are a bit skinny and don’t have the internal cable routing. I like fatter hoods .. like on the 105s or Campag or SRAM.

Rival is at least 105, Apex is more Tiagra but it’s nearly as good as 105 in my experience.

The front mech sure shifts a whole lot better

Rival brake levers / shifters not cheap (retail price £325)

Tiagra STI brake / shifters more affordable (retail price £209)

=disparity in groupset comparison, Rival closer to 105 across the groupset

Rival very nice for riders with smaller hands (or ladies)

Shimano can feel too bulky for bikers with smaller hands, even when using the rubber shims on the STI units