to be honest i dont know much abotu either of them. Hondas are reliable and everything ive read about atomik's is shouting stay away from them. So i would do exactly that, buy a honda. Its a honda after all, its one of the major motorbike manufacturers in the world, prob one of the best and it has racing pedigree. what do atomik have? Bad rep bad rep bad rep bad rep bad rep and some questionable looking bikes. Some mind you.
Plus with the honda, stick 125 honda in it. Cheap as chips for a honda engine these days, where as a new pit bike engine will prob be a bit more. in the uk anyways.