To answer your questions:

1. What class is the Edge? It's a Class F, Intermediate SUV. On the main Avis forum, there's a thread/sticky "Avis Fleet List". It's not guaranteed to be accurate, as it's only as good as the info I/we post here, but it's pretty good. Also, when you return your vehicle, you can look at your Avis.com profile/receipt and it'll show you what class you were given & what you paid for.

2. Were you given the upgrade b/c of Preferred status? That's hard to tell. Possibly they were out of "Standards" (which have very few car models in that class, BTW); possibly they were being nice with an upgrade due to your status or b/c you had a high daily rate; possibly the Edge has been sitting there unrented for a bit and they wanted some miles on it, etc. It's hard to know their reasoning unless you speak to the person in charge of assigning cars to renters.

PS: That is one of my favorite cars in the Avis fleet... enjoy it! It's not too big, but has lots of interior room; the seats are mighty comfy (totally opposite the other crossover that Avis like, the Vue), the ones I got usually had quite a few options, great handling, etc.