Personally: I choose the smallest one I can get away with. Only powering the fridge, furnace or lights. Transfer switch installed, I can run either or all three items. I use a older Coleman 1850 (surge) generator. runs many hours on a gallon of gas. Portable, about 65 pounds I think.

I'd hate to run a big generator that sucks gas for only a few items when a smaller unit will do.

I'd get the e2000 that Wulf202 suggest. I'll get one too someday. Great product. Just $$.

One just like mine on craigslist for $200, can't beat that deal!
http://denver.craigslist.org/tls/3336317882.html