Keycap Profiles

• Cherry → keyboards of Cherry brand (Cherry is a German company).
• OEM → Original Equipment Manufacturer. It means, a typical cheap keyboard.
• SA → “spherical angled” or “spherical all-rows”, from Signature Plastics (a USA company that makes keycaps).
• XDA → Not sure what it means.
• DSA → Not sure what it means. Probably a name originated from Signature Plastics.

Basically, key profile are of 2 types:

• Uniform → all keycaps are shaped the same.
• Non-uniform → Each row has a different shaped keycap.

There are 3 shapes of keycap's top:

• Flat
• Spherical (concave)
• Convex. (usually for the spacebar key.)

Another issue, is how the key plate is shaped:

• Flat. (like laptop.)
• Staircase. (like a mechanical typewriter.)
• Curved (Concave. Like Kinesis Advantage2)

Conclusion

I think the best key profile is uniform with concave top. Concave top helps your finger determine position of the key. Uniform is great for swapping keycaps.

Those non-uniform keycap profiles are a hack, to make up for flat key-plate. We should use a curved plate if one really want a ergonomic fit.