Is guthans NMZ the best and fastest way? Is there another method but costs a little more? How long would guthans take?
It depends, guthans is NOT the fastest, get rockcakes, overload at 51 hp, then ur at 1 hp, drink some absorptions and dh on hard mode in nmz, thats over 100k xp an hour (rapid click your rapid heal prayer so your hp doesnt go above 1).

