There's a bunch of DSPs out there but the only ones I consider are those that also have a relevant share of what you buy coming from their own SDK, on top of "how well" the ML works.
The only ones I'd consider working with are Moloco, Liftoff, Mintegral and maybe DT.
Kayzen built a very good product but their algo is still not the best (they have other advantages though). Smadex is another good one but still not at the levels of their competitors. Additionally this last two picks don't have their own SDK traffic.
Another thing to consider when you evaluate DSPs is that they more or less have plugged all the same exchanges, so you'll buy theoretically the same traffic. That's why owning the SDK moves a bit the needle for me.