Like BLKKROW, I like the E3Dv6 but can't say whether it'll make any difference with your issue. I switched to the E3D as part of a rebuild that centered on using Smoothieboard instead of Arduino/RAMPS, so it's hard for me to offer a comparison. My main reason for liking the E3D is the way it seems to be a fully engineered product, with all engineering drawings being available. From what I've seen of broken hexagon hot end pictures, I think the E3Dv6 has a better thermal connection between the heat break tube and the hot end heatsink.

IIRC, the E3Dv6 tip is a bit shorter - I assume that leads to the smaller heat zone. Rather than a smaller heat zone leading to less pressure build up, it probably allows the pressure build up to deplete/recover quicker. As another option for you, I believe you could install an E3Dv6 tip onto a hexagon hot end and experiment with that.

Also note that the overall length of the hexagon hot end apparently isn't tightly controlled. A few people have ran into issues with their two hexagon hot ends for a dual extruder not being the same length, although I believe clough42 now provides an adjustable backplate that allows you to compensate for that.

For your rounded corner issue, I'd do what I could to rule out any possibility with inadequate print cooling (if PLA), a bit too high of temperature, or a bit too excessive extrusion. Just to throw options at you, note that Simplify3D offers two settings potentially related to this - "coast" defines how far away from a movement end the extrusion is stopped, and the "wipe" setting can be used to actually back the nozzle up at the end of a move and then wipe it back over the end of the extrusion again.