The s6 edge plus is one of my favorite phones ever, but the one thing it isn't is comfortable in the hand. The s8+ is far more comfortable to hold due to the curves on the back and sides of device. Even the s7 edge improved substantially in this area over the 6+ and the S8 is more comfortable than the s7edge.
the only question is reaching the fingerprint sensor and top of screen. If that is a concern, just go with the s8, even it has a larger screen the the s6edge+.