To be honest with you I think you've exhausted the list of browsers I'm aware of. Out of the four I think Chromium might the one I have had the most luck with. I would certainly be interested to know what the "bug" is.
The issue is maybe not so much the browsers but the device they are running on. The Pi 3 is by no means an underpowered device but loading webpages can be really resource intensive. I'm not sure what you are defining as content heavy but even on a fairly simple site there is multiple things that might need to be loaded.
JavaScript is probably the main culprit with regards to slowdowns on webpages loading. Installing some kind of adblocker, (depending on if you deem it ethical or not), would reduce the amount of information that needs to be loaded. You can go one step further in Iceweasel/Firefox and install an extension called NoScript from https://addons.mozilla.org. This will block any JavaScript from running and should lead to a speedier web browsing experience.
Also worth keeping in mind is multitasking, having multiple tabs open at once can have a dramatic impact on overall performance. Try to avoid doing multiple things at once or in really quick succession. I wouldn't recommend having more than 5 tabs open at once in any of the web browsers. As you have discovered that requires lots of RAM.
In general don't expect the same web browsing experience on a Pi as you would a full desktop computer or even a smartphone. The Pi 3 is leaps and bounds ahead of the original model, but don't expect it to perform like a more powerful device does.
