Each mfgr. touts a different angle on their windows. Some are clad in vinyl, others aluminum, and others are all wood (no clad.) So, what you might want to do is get the paperwork on each and then go talk to the dealers. Ask Pella why you shouldn't buy Anderson and Marvin. Ask Anderson why you shouldn't buy Pella and Marvin. And so on. Once you educate yourself (as you're trying to do), you'll be able to make that educated decision.
My best to ya and hope this helps.
PS: There are certain brands that I favor over others, situation depending. For example, I'm partial to Velux for Skylight windows. But overall, with 2 brands being equal, it's taste and quality.