That's easy- the MXR EVH 5150 pedal is way all around better for newer metal tones! It's also a much newer design. Distortion pedals have come a long way in 10 years. It's got a serious amount of ripping gain available, but also sounds great set lower for more dynamics, of which there are plenty. The 3 band EQ allows a lot versatility, from scooped and twangy to fat and throaty. Plus , it handles every kind of pickup with ease. It's an excellent high-power distortion pedal.
I haven't played the MXR, but isn't it supposed to replicate Van Halen's Marshall plexi sound, were as the Wampler is supposed to replicate a Mesa Triple Rectifier. Like I said I've no experience with the MXR, although every other MXR pedal I've played has been fantastic, so I'm certainly not saying it isn't going to get you there, but the Triple Wreck is definitely going to be able to give you as much gain and low end thud as you're ever going to need. You might also want to give the Amp Tweaker Tight Metal a look.