I was just going to say that(about Crays) Sunner, looks like you beat me to it🙂(BTW- They still use MIPS).
I would say the *best*, all things considered is the Athlon T-Bird/Duron, though that is an ever changing thing.
Best overall performance, size, heat, actual application flexibility, and cost be d@mned, then the Alpha.
Best "breakthrough" for the masses then the 386(followed closely by the P6 core).
Most scaleable, IBM's "Power"(a souped up PPC) chips(see Deep Blue and others).
Best value, tough call between current Durons and the Celery 300A.
I can't pick one winner, it is like asking which is the best car ever, it depends greatly on what you are looking for.