Look, 250 watts is a lot of power to be pushing through a coil. It doesn't really matter what
tank you use, if your wicking is off or your cotton isn't saturated enough, there's going to be burnt wick. Your best bet is probably to invest in a decent RDA, that way you can keep painting the coils with
juice. Something like the IJoy Limitless RDA. As far as coils go, take your pick of the big boy offerings -- framed staples will probably work well. Just make sure you are using good batteries and there aren't any shorts.
Alternatively, if you really want a tank, you could purchase one of the Smok TFV12s. I think they have one or two coils that are rated for 250 watts and, for the most part, can work at that wattage. Obviously you aren't going to get the same flavor as you would out of a rebuildable, but it'll be a hell of a lot more convenient.
I can't really think of a single RTA that I would suggest someone vape at 250 watts. The closest thing I can think of, and I'm not even really suggesting it, is the 30 mm Aromamizer Plus -- simply because it is actually an RDTA so you can drip
juice directly on the coils and the build deck is massive enough to handle the kind of coils you'll need. But I don't think you will get many non burnt 250 watt hits off of it without dripping into the chamber.
Good Luck.