Over about 400bhp I'd use IK31, under that IK27.
It's not really a case of what's best, the IK range like other precious metal type plugs do tend to be a bit smoother, and slightly sparkier lower down, but also ime tend to be much much more sensitive to rich mixtures and fouling from which often they don't recover, whereas a 077 is a very hardy plug and shrugs off this same treatment, for my money I'd use Ik's, I'm just using 077 whilst running in.
tabetha