Pretty broad subject matter there. Can you narrow it down to what you are looking for with regards to look/feel and then we can point you in the right direction from there?

Most pro’s would agree that “ high end vinyl” would offer the best return on investment as well as being the most energy efficient. Cheap or low grade vinyl will not offer anything.

where are you located as that has a lot to do with specific brand availability?

Nice advice there, Window1. What window salesman or company is going to admit that their vinyl windows are anything less than "high end"?

I'd agree with WoW, that's a pretty broad question. My recommendation would be to establish your goals for the project and what you value more (ie: appearance, performance, warranty, maintenance, cost, etc). At that point, you can funnel down to a material that best fits your needs (wood, vinyl, fiberglass, metal, etc), and then establish quality choices within that material. These choices will often be regional as well. As Buzz said, everyone will say that their product is "high end", however, obviously that is not always the case and that is why the OP is doing research as opposed to simply having a couple contractors out to her home.

“Nice advice there, Window1. What window salesman or company is going to admit that their vinyl windows are anything less than "high end"?”

Opposed to your useless advice??

The OP is smart enough to ask us questions on this forum so she is probably smart enough to ask us which window brands she may have been presented with that that we consider “high end”. I dont think there is any calculous in that assumption Buzz Lightyear.