You've got to just compare prices and terms of consolidators vs. direct with the rental companies. i would think that their insurance packages are actually those of the rental car companies they're working with.
I've gone through AutoEurope.com, a New England company, and selected pickup locations that I knew belonged to Hertz. And AutoEurope beat Hertz' price somewhat.
Remember that if you're going into Italy, you're going to have CDW insurance by law, and you certainly want theft insurance on the car for there.
Remember that not all familiar rental car companies are the same in Europe. I've read horror stories about another big name rental company in another part of Europe. Sometimes the rental companies in Europe are franchise operations, and you may not like dealing with them.
I've had good luck with Hertz and AutoEurope.com. There are other consolidators that I'm sure are good at what they do.
Your Germany/Austria/Northern Italy is my favorite part of Europe to just ramble from town to town looking at the mountains by auto. You will have a great time.