Just to clarify, there are "quick-release" racks AND quick-release cases.
The most basic and least expensive Pelican-based case system would consist of a rack that is permanently mounted to the bike with Pelican cases that are permanently bolted onto the racks. Both the rack and cases stay on the bike (unless you want to unbolt everything)
Another option is to use the same permanently mounted racks, but use a quick release system to remove the cases. This is how the standard Caribou system is set up. The Caribou rack stays on the bike, but the cases are removable using their own quick release mechanism.
You can also accomplish the same thing with other racks like the Givi or SW-Motech and use the Twisted Throttle quick-release kit. I think the quick-release mechanisms are fairly similar for both, so if your choice is based solely on the release mechanism, I think it's a toss-up.
Finally, you could also have BOTH removable racks AND removable cases. This is what I prefer and how I set mine up. AFAIK, you can only do this with a Givi or SW-Motech removable rack combined with the Twisted Throttle quick release case kit. As soon as I say that, somebody will correct me. But if we're talking about a Pelican case type of system, this is the only way I know how to have both removable (unless Caribou has now made one)
I originally chose to set mine up with Storm cases (now made by Pelican) permanently mounted to SW-Motech quick release racks. When I wanted to remove the cases, I simply removed the quick release rack and the cases came off with the rack portion still attached. When the Twisted Throttle kit became available, I bought it the first week it was released. There were some minor fitment issues on my DL650 that I reported back to TT. I corrected the fitment problem on my own, but I notice that TT now offers a kit for the DL650 that eliminates that particular fitment issue.
I now have the ability to easily remove the cases AND/OR the racks and I'm very happy with the setup. The TT kit is not perfect. It is quite heavy and the locks are only so-so. But in the end, I think it's fairly comparable to the Caribou setup for less money, plus I can use it on a removable rack which is a bonus.