I have noticed that the stainless from brand to brand can be a little different. But if you want to mix brands you could always use a cabinet panel on an appliance too.

I just had to replace the refrigerator in mom's home so we just changed out all appliances. We ended up getting same brand as some (cheaper) ones were not the same. They looked mismatched. So I guess if you want them to match I would get same brand and if you want to mix it up then different brands are fine :)

I have different brands of everything, but if there's a difference I never noticed. I have Wolf, Thermador, Bosch, and GE Monogram in the same small kitchen. Perhaps the higher end brands are more consistent. I don't know, but it looks good to me.