I test rode at least a dozen bikes, and test rode tiagra 10, 105 11 and ultegra 11 extensively.

From what I could tell, there are no differences in shift quality between the three component groups.

I haven't bothered getting the citation, but there is a recent mtn bike publication which compared Deore vs XTR and found the shift quality was identical.

Shimano is so dialed, it's really kind of ridiculous at this point.

Even Sora 9, and 8 before that with the thumb shifters, were superb.

Shimano has perfected cabled, indexed shifting. Hyperglide, introduced a quarter of a century ago, offered essentially perfect shifting under load.

You don't ever have to worry about shift quality with shimano, esp. with rear shifting. I consider tiagra10 front shifting to be very good to excellent as well.

Shimano componentry is the best.