Typing experience is the first thing to consider in mechanical keyboard.
That's why hardcore people always looking for the best for their fingers.
Usually starting from the switch.
Linear vs Tactile. Best linear would be vintage black and the tactile one should be mx clear.
while i agree mx clear is a good tactile, but blue/green is a great option as well! 
Springs - stock springs not so nice - 55G/62G korean springs will be the best.
Lube - A must for the best feeling out of your fingers.
Not for mx blues! 
Stickers - Eye candies. Less wobbles, for people can feel it.
Plate - just metal/alu plate.
Casing - Metal casing is a must too (P/S I should recommend this first before anything)
Memory foam - Another little things, but giving great effect. It dampens the sound a lot. Quite noticeable. But you can't use too thick as you will feel like typing a keyboard on sofa.