I say amp. Modelling and pedals can only get you so far if what you're after is a high gain metal tone. Nothing beats a cranked tube high gain amp, because a)when close to full output tubes produce natural harmonics and overtones which give the tone "life" and b)the speakers also have a distorting threshold; if you drive them hard you will get a better sound. But realistically speaking, cranking any tube amp is not a good idea unless you're gigging or at a jam studio. Or don't live in an apartment, heh.
And another thing, if you want metal, it has to be a humbucker equipped guitar. Single coils just can't produce the type of sound you want to get out of them.