Kirby's Dream Land
Kirby's Adventure
Kirby's Dream Land 2
Kirby Super Star
Kirby's Dream Land 3
Kirby 64: The Crystal Shards
Kirby: Nightmare in Dream Land
Kirby & the Amazing Mirror
Kirby: Canvas Curse
Kirby: Squeak Squad
Kirby's Epic Yarn
Kirby Mass Attack
Kirby's Return to Dream Land
Kirby: Triple Deluxe
Kirby and the Rainbow Curse
Kirby: Planet Robobot
Kirby Super Star Ultra
Kirby's Pinball Land
Kirby's Dream Course
Kirby's Avalanche
Kirby's Block Ball
Kirby's Star Stacker
Kirby Tilt 'n' Tumble
Kirby Air Ride
I like to split the series into the goofy and the traditional. The offbeat games are just too different for me to really stack them up. As far as the traditional ones go, my favorite is Kirby's Adventure. The remake is good, too, but I don't like the changes in the physics in that game, with the standard walk but the immediate running jump. It's not very consistent. Physics are also my gripe with KDL3, the way when you exhale you drop straight down. It really messes with the flow of the game.
I think my next one is probably KSS, although I love KDL2 as well. But the 3DS games are probably better than it KDL2, and Return about even. Kirby 64 is all sorts of underrated, and Squeak Squad, Amazing Mirror, and KDL bring up the bottom. The mainline series is remarkably consistent in quality, though.
On the opposite end of the spectrum, Mighty No. 9 exhibits some of Inti Creates' worst design habits. The biggest issue is the sheer number of instant-death traps, including stages that can't be cleared (as far as I can tell) without a particular weapon in tow, and blind jumps with spikes at the bottom. On top of that, I've run into at least one boss with an instant-kill move, and in a game like this, that's no fun. They really should have figured out the balance was off when they compensate by having a little robot give you a crapton of power-ups upon dying, one of which is potentially an extra life.
I may see it through until the end, because the dashing around is a lot more fun than I anticipated, but dang, if the game isn't full of the sorts of unfair difficulty that Mega Man is just occasionally guilty of.

