Ok, I'm really torn right now. Just yesterday I more or less scratched the S8 off my list for its RAM management issues, but now that I tried my commute with my main SIM (which has unfortunately spotty coverage at times) in the S7 Edge, I noticed that it stayed connected to LTE much better than my iPhone 7, so it looks like I might actually do quite OK with a single SIM phone if the antenna is just good, and despite my earlier impression, Samsung seems to do quite fine in this department.
I have some concerns about the S8 still. The fingerprint scanner placement is one, but it sounds like people have gotten used to it after the initial shock. Then there's the RAM management issue, which is hopefully solved by an update, but it's still something to keep in mind. Finally we have the utterly useless Bixby button. Why, Samsung, why? Not to forget Samsung's constant habit of dropping the ball with updates, but there's some hope that they'll finally learn.
However, I would still like a waterproof phone equipped with a good camera and a headphone jack, and preferably something that doesn't take ages to charge and can actually provide me with modern smartphone functionality such as mobile payments. If the OnePlus 5 fails to deliver (I'm most concerned about waterproofing as it looks like they've finally done something to the camera), the S8 is enticing despite all of its flaws.