Mechanical keyboards have several (clicky/thocky/tactile/linear/etc switches, Cherry MX Browns, etc), but if I had to choose one, maybe ortholinear vs staggered.

A picture will probably illustrate it best:

Ortholinear evangelists contend that the staggered layout was invented for mechanical typewriters exclusively to reduce the incidence of typebar collisions and is detrimental to optimal ergonomics. I, as someone who prefers staggered keyboards, just don't want to be ruined for the majority of keyboards out there. (If my muscle memory "learns" that "m" is "here" because I use an ortholinear keyboard at home, I'm worried it'll be awkward to use a standard keyboard on a laptop or whatever and I'll be fat-fingering keys all over the place.) I might switch sides someday. Who knows. But for now, I'll stick with staggered.