Everyone's forgeting that these pedals can be modded (especially the metalzone) to sounds that are way better than the stock sound. I didn't think it could make a difference until I got my hands on a modded boss ds-1. Side by side with the stock pedal it makes the stock sound like supreme crap! And a modded metalzone kicks the crap out of a stock metalzone. Don't believe me? Check out http://www.kmdes.com/pedalmods.php
He does pedal mods, and for cheap too, or you can just buy a brand new one if you don't already have one. Yeah, a boss ds-1 modded costs less from him than from the local radio shack. He doesn't have the Metal zone mod on his site, but ask him, and he'll do it for you. It's so great, I can't even play stock pedals anymore. Now if I had more money for a phase 90 mod.
And yes, both have their ups and downs, the metalzone is amore classic 80s distoretion and the death metal is for new types of metal. I'm not sure if the digitech pedals would be so reliable, but the bosses are built like tanks. They are both different pedals really meant to do certain things. If you put the boss mt-2 vs. the boss hm-2 then that';s a different story, the hm-2 sucks, but that was what the metalzone was before it became the metal zone, it even has the same colour scheme. Just remember, go with your ears, buy what you like, but don't just limit yourself to 2 pedals, there's more out there.
And if you're low on a budget, yeah even I'd go with a death metal. It is good for the price.