Real leaf switches or go home

Seriously, it depends on your bank account, what kind of games you play and what you are willing to live with, where performance is concerned. Just remember, just because the marketing guy puts the word "leaf" in the name of a button, it doesn't mean it uses a leaf switch. Some of these use a typical "keyboard switch", with a simple bent piece of metal inside for it's contacts. I.e. not a leaf switch.
There's only one type of switch which is actually a "leaf switch", and they are not mistakable for any others either in appearance or performance. Real leaf switches are not only adjustable to get just the response you want, they have very unmistakable performance and feel characteristics which no other switch can provide. They also typically last 20 years or more, if properly used.
Buttons are just a way to actuate the switch. Concave, convex, it doesn't really matter that much. There is a small bit of utility in the finger-to-plunger shape, but both serve the same purpose. In the end, it's mostly cosmetic and preference. What's really important with the buttons (without considering the switch) is ease of installation and switch-less spring strength. If it's too stiff, it'll probably get tiring during long play sessions. You just don't want accidental actuations. Higher than that is probably too stiff.
There are a ton of options. Explore as many as you can and pick from there.
