Asking me for an opinion without stats? Asking the wrong man.
But... it's a close one, a very close one. Both are the same age, both are in good form. However. On one hand, Soldado has a better scoring record, that much is undeniable. On the other, Negredo is more than just a pure finisher, and a brilliant all-round forward capable of playing any kind of role at all, as well as being physically more imposing and likely better suited to the Prem. On top of that, he's likely available for cheaper. Soldado's an excellent player, but in my eyes Negredo takes it, if only because of my massive Negredoboner.
Then there's Lewandowski *LewandoBoner*...........