A requirement is a steady unit that you can push against. The capability to tilt and crank are also handy. Talens and Maimeri models now have electric elevation and inclination. Often, having more than one easel is a source of creativity.
Different offices yield different business.
I've worn out and buried three of those beautiful mahogany French ones, as well as a couple of folding table-toppers. When backpacking I use a Churchill cigar-box, clipping 8 x 10 inch hardwood panels to the inside lid. My studio easel is one my dad helped me build 20 years ago. While there's a sense of continuity when you paint with a time-honored design, it's also useful to work with one you might build yourself. The impressionists, particularly, were an inventive bunch.