Both good varmint cartridges, and I think the 204 is catching on pretty well. This means availability of factory ammo, components, etc. will become more readily available.
Of course, the 22-250 is well established already. The velocity advantage to the 204 is
slight, but the 22-250 pushes a little heavier bullets. With bullets of comparable weight there's really not much difference between the two.
I'd be inclined to go with the 22-250. The use of heavier bullets will make it slightly less subject to wind deflection, and will make a better varmint cartridge when it comes to the larger critters such as coyotes.