When there’s need to record velocity, I like soft/squishy matter for some reason.
Otherwise OP-1 solid rectangle keys are all good
I’m not that fond of lines of square or round Elektron buttons : I like buttons that are wider on the Y axis than on the X axis.
Fingers are not meant to be aligned.
I prefer something slightly soft/rubber, like roland sp pads/buttons. Elektron buttons feel kinda cold/non musical like a computer keyboard. Slightly off topic - really not a fan of the elektron knobs either. At first I liked them cos they felt expensive/solid/different. But after having them on OT and now AK they’ve started to feel kind of soulless and remind me of etch-a-sketch… But just little niggles, all ‘works’ great so no real complaints…
The ones one the TR-808 are a bit slow but can be nice big clunkers as well. Forget space. Who needs that? They feel nice but not always reliable when you need speed.
I like the ones on the Sonic Potion LXR. Immediate and direct with an led near by on the panel. Like the Elektron buttons but without the clinking sound.
I also like the squishy back-lit ones on the korg micro kontrol. Might be the same on the new elektribes. Of course MPC pads are nice too (My experience has been MPC 2000 and later).
Squishy wide buttons with the led might be the best. You can get the feedback in the button saving space and the ability to have velocity sensitivity using different parts of the button. But if it’s one force function go with a smaller button with an led near it.