Yea, but a lot of people prefer strict alternate picking because it has almost like a metronome feel to it if you get what I am saying.
To the threadstarter:
Also depends on the sound that you are looking for. For that thick chunky riff work, downpicking, but alternate picking triplets and such because no one can down pick that fast, not even hetfield. Just be careful, I got tendinitis and have to sell my guitar before I make it worse. I'm gonna start back up with a cheaper guitar, but am pissed because my guitar is the same exact one as Patrick's so I actually feel like I'm good, hahaha. J/k.
For shredding most people tend to use complete alternate picking as it gives that metronome feel and is a tad bit easier to keep in time once you get used to it. However, strict alternate picking, even though a powerful tool, is nothing when it isn't used in conjunction with other techniques such as legato or sweep picking.
yeah i love players like petrucci and gilbert, which use strict alternate but i love michael romeos technique much more, not saying i love his music more, but watching his instruction video makes me extremely happy in the pants.