(Points about marketing and such above - I'm not one to typically buy into the marking hype from the bike industry)

I have 3x9, 2x10, 2x11, 1x11, 1x12 setups.

In terms of my road bikes - my least functional group set is the 3x9. Cross chaining eliminates many of the gear combos - the granny gear isn't all that "granny" - I have to shift the front far more often to avoid cross chaining. The only reason I've not changed it - the aesthetics of the old Ultegra group set just fit the bike better. IMHO the newer stuff just aint as pretty.

The 2x11 with a 34x36 granny ratio, for me, is far superior in every way than the 3x9. I can do entire rides, even in rolling terrain, without ever shifting the front. Can even ride the 52x36 on the stock chain and rear mech - and cross chaining effects are minimal at best. For pure climbing - the 34x36 gets my weight/watt challenged self up the biggest mountains around. And for a really flat flat ride, I can easily swap out for a 11x28 or 32 rear for smaller gear jumps.

1x - like them for gravel, really like them for MTB. The 1x12 on my Stumpjumper has crazy gear ratios - I can power up just about anything, and struggle to turn the biggest gear at higher speeds. Plenty of gear options on both ends of the cassette, and everything in between.

The 3x is at the bottom of the pile for me, and only staying on my bike because of way the crankset looks.