There is no "best". If you are lucky there is a "best for me", but there may not even be that.
Personally I don't want a large phone. So of the devices released so far this year the S10e is the one that would be of most interest to me. But Samsung's software is still bloated, they are very slow with major updates, their camera processing is not as good as Google's (though I've real cameras for that purpose) and their UI smoothness isn't up to the best around. If I was a gamer the Exynos' gpu not matching the S855's could be an issue, though less so with the lower-resolution display than with it's bigger siblings. Some of those are nit picks (or are to me: they might be deal-breakers to someone else), and it's certainly a device that interests me, and it would be a strong candidate if I had to do an emergency replacement of my phone this week (it would probably be that or the Pixel 3, TBH). But I think it would be premature to call it as "best" at this point.
So what are the other candidates? We don't know, because right now there are only rumours of varying degrees of wildness. A smaller Pixel 4 might be a candidate, and certainly wins on the software front, or maybe Google will screw the design in some way? Maybe Essential will rise from their coma and release a PH-2: the original device wasn't perfect, but it was ahead of the competition in many respects, and their software support puts all of the big OEMs to shame. Maybe Nokia will release a reasonably-sized mid-ranger that provides a well-balanced device with good software support for a third of the price of a big brand flagship and that will get my vote ("best" should not just be about bleeding-edge specs and bleeding-you-dry prices, so there's no reason that accolate must be reserved for a flagship). Maybe someone will come up with something that's a real surprise?
In short, ask me in December and I might be able to answer. But most likely I'd still name maybe 3 devices for different reasons.
