eVAC and eVent® Compression sacks are basically the same. One has a compression harness, one does not.
The Granite Gear Uberlite bags do not come in a compression variety.
All three do the job keeping things dry. I have had my eVent for about three seasons with no discernable water problems, even in an open topped canoe in two days of rain. I have no long term reports or experience with GG's cuben bags. Bothe are available in the sizes I need, about 10L.
Of course compression sacs are inherrantly heavier by about an ounce or so due to straps, buckles and mounts. This is ofset by the reduction in volume for my sleeping bag and bag liner (a set of long johns and socks.)
Lighter Cordura bags don't seem to hold up as well for my use. Cordura makes good tarps, but it usually fails to make good dry bags. Too many items in the pack are odd shaped: pot, stakes, buckles, etc. They don't take abrasion well, but they DO work well for about a week. If you are searhing for the lightest weight bags, these are the ticket. But be prepared to purchase a new one for each trip. Seams stretch, fabric can stretch, and, thay can be easily punctured, example: by a stray stake. I bought a set of three that all leaked after a single week, but not the first or second day, usually. I simply seal them with a mineral spirits/silicone calk mix and they hold up better. But, I loose the weight advantage after the third application. I use these as my food bag usually, knowing my food is usually in ziplocks.
I used to carry seperate bags for ease in stuffing into stow wells of kayak. The pack was often rolled up and stuffed in the back with various pieces of gear in it (fuel, stove, pot, cover, wind screen, flashlight, bear line, etc...) At a long portage, I will simply drop the bags into the pack, put the wheels on and go. But it has been over 20 years since I was out in a kayak. Mostly I use a smaller 12'6" or 13'8" stripper canoeyak. The pack, I leave loaded, behind me, under the rear spray-deck. Here is a picture from the St. Regis Area in late July.
As you can see, there is only the canoe & gear that is different. I had 2 bags with me but the food bag was down to about 5-6 pounds by then. Using the pack prevents a lot of wear on the bags, too.