I'm not a fan of the big top boxes like the OEM one, or the one shown in post #6. Most of the dislike is just plain aesthetic; I don't like the look of a big bulbous box sitting up on the end of the bike. You have to exercise more restraint when it comes to packing for a trip, when you have all that extra space, and resist the urge to fill that space to the brim. I don't recall the load rating for the rear luggage rack of the S10, but it probably isn't more than 20 lbs.
I started off with the OEM panniers for the S10, but probably had them on the bike for less than a year. I found that I didn't really like top loading cases, especially on a loaded trip. Having to unpack the stuff in the case in order to find something at the bottom was a drag.
Ultimately I reused a set of knockoff Pelican cases that had been on my previous bike, a V-Strom. They were marketed under the Duratool brand name, but there were actually just Chinese imports that I've seen sold under a different name at Princess Auto. They were probably 40 bucks apiece way back when I bought them around 2013, and between the two bikes, they've seen well over 100,000 miles of use.
The setup looks like this:
They don't have built in locks. If I'm on a trip and I have to leave the loaded bike for any extended period, I have cable locks I use that both lock the lids and also lock the cases to the pannier racks. Most of these Pelican style cases have padlock holes in them. I'd say that my setup is at least as secure as the built in lock you'd find in any of the plastic boxes like those made by Emgo or other similar ones sold on Amazon.
Harbor Freight sells cases similar to the ones on my bike, under the Apache brand. Their largest case is slightly smaller than the side cases I have. I've examined the Apache cases, and they're very well made, probably superior to mine. If I was in the market to replace my setup, I would seriously consider theirs.