No manufacturers are selling single pane windows. All offer double pane with low-e and argon, and some will have two or more versions of that with a single coat of low-e, a double coat, different types of low-e (hard vs soft coat), low-e on different glass surfaces, etc. As a consumer, what you want to look at is not necessarily the details of the type and location of the low-e, but what the thermal performance ratings are, as that tells you how the glass will actually perform and how those details will actually affect you.
In Indiana, you'll want the u-value as low as possible (I like .28 or lower from a double pane), with a moderate shgc of around .27 or higher (it can be lower in a triple pane package).
To proceed, ask both installers what the u-value and shgc of the window that they are proposing is, and also ask for the CPD #, which is the certified products directory on nfrc.org. You can then look the product up and verify those numbers for yourself.
I don't deal with Polaris much, but I'm pretty sure that they offer more than one double pane glass package. That said, there are all different kinds of "dealer agreements", so it is possible that the guy that says he can only get that one package may be telling the truth.
Have you gotten a quote for the UltraWeld? I like it a bit better than the Thermal.