I'm so confused!

We have a nice big bay window on the front of our house that we've decided to replace. We've had three companies quote so far and another one is coming tomorrow night. Of course every company is telling us that they have the best quality windows and best installers.

It is so hard to compare apples to apples because everyone is telling us something different. Just as an example, one company told us that a stainless steel frame between the panes is good because it won't bend or warp over time. Another company told us that stainless steel between the panes is bad because it absorbs extreme temperatures and the cold metal will create moisture between the panes in the winter. They use insulated vinyl instead of steel.

What do I need to know? What should I be looking for and what should I be avoiding? Can anyone help? I know nothing about this process and the research that I've done so far hasn't helped much. The one thing that I have made sure of is that all of the window brands that we look at are Energy Star rated and government approved. Thanks.