Quality[/b] – Go with Wool if you can afford it, a blend with up to 40% man made fibers is OK if you are cash strapped. Wool is sought after because it maintains its shape, retains heat, absorbs moisture without showing, and it has the look other fabrics are judged by.
Bad advice. You can get a 100% wool suit at Target for $150, why on earth would anyone recommend a poly blend? Wool is sought after for a lot of reasons- depending on the type of wool- but polyester (aka microfiber, aka synthetic blend, aka man made fiber) is HOT, shiny, and drapes funny. If you're "cash strapped," figure out your measurements, identify some timeless designers, scout the thrift stores in the rich part of town, and befriend a local tailor. shouldn't have to lay out more than $60 for an extremely high quality contemporary cut tailored conservative suit (though for some reason it's often hard to find solids, almost always subtle pinstripes).
That said nobody's gonna remember what you look like- let alone what you were wearing- as long as it's nondescript. Change the tie and worry about the interview itself.