I'm having 24" Magnaflow muffler welded in in place of my stock muffler. I don't think I'm going to change anything else... should I get a stainless or aluminized muffler?

 

stainless.

I've heard aluminized rusts very easily

 

Hmmmm.... I thought it was supposed to hold up pretty well. I don't really care what it looks like because it's going to be tucked up out of the way.

 

Go with stainless! For the difference in price it is well worth it. Never rusts and is gauranteed for life. BTW, I would recommend getting the 5x8 18", it sounds so nice and the performance gain is definetly noticible. The muffler is 24" total with the end sleeves.
Another option is to put a magnapack resonator if the drone is too much for you. I have a friend in the exhaust business, and he uses this method with the Magnaflow if customers don't like the growl.

 

I actually have an 18" body Magnaflow(sitting in the box), but everything I've read tells me that it's a little loud in the cabin. From what I've heard on Cory's page, the 24" is pretty mellow, but still sounds nice and doesn't drone in the cabin. The performance should be the same since they are both straight through.

 

I love the sound of the 18". Makes my truck sound deep. Trust me, you won't sound like a weed wacker on steroids!

 

Definately get a stainless if you are within the rust belt!