I have always sat in a chair. A nice desk chair on wheels would be nice for moving about a little more...but depends on the set up. My next set up will be for this.
I do use a bar stool with a swivel top for my set up with my rifle rack/vise for mounting scopes, etc., as my tool box is set up to the right.
I stand. I move back and forth going from powder dispenser to the press. I pour the powder in the case and put the pan back, while it is throwing the next charge I am seating the bullet on the previous charge. I load small batches and the process works well for me.
I marked sitting do to that is how I was taught to do and I have my scales and other tools at tabletop or eye level.
My primary loading table/ countertop bench is mid height and 6' long with 3 presses on it, 2 Dillon 550's and a RCBS rifle press.
To look at my set up you would say what a mess, but everything has a place and it is returned to that place.
As for seating I use an adjustable height office chair on rollers and roll from place to place as needed. I started out with a regular office chair but got tired of having to move it from station to station. I have shotshell press on a drafting layout table and a old washstand fitted with a tabletop as general purpose work bench with a vise mounted on it with most of my gun cleaning/repair equipment tools.
The only time I stand is when I anneal brass cases or remove cases from case cleaning equipment.