I wouldn't (or I didn't) worry about the engineering differences between the racks. For me, the main concern was being able to carry the gear that I need to carry. I started out with a standard-sized rack and quickly discovered that I would heel-strike with almost any load. I switched to a expedition rack and finally had enough room for my heels (I think it's a Jandd rack but my bike is in the shop so I can't confirm that).
I carry a garment bag pannier and hang a reusable grocery bag or cooler box off of that for my lunch bag. Together, that probably weighs about 25-30 lb.
In summary, I would more worry about budget, fit (on the bike and you+rack+panniers), and weight capacity.
A nice feature to have on a rack is a built-in light mount but this is entirely up to you on priority.