For what it's worth I went with Nation Wide as they offered 3 years of full replacement value which is better than the standard cash value. Not knowing the future values of Tesla I thought this was the best way to go in case the car is ever declared totaled. In this case I will get my purchase cost back.
Woo. I should actually look into that. I didn't find any full replacement value options when I was looking.
Being in an annoying time crunch, I ended up going with GEICO, which was 25% cheaper than the next competitor for my particular driving record and location (NY). Interestingly, the vast majority of the cost of the insurance is collision and comprehensive -- that's the expensive aluminum-bodied car, I'm sure. The cost of all the liability and injury related stuff was very small by comparison.
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Most of them just wouldn't even quote it. He told me go with Geico, check back in a year after the lazy companies get data on the Teslas after they've been on the road for awhile.
This was my experience in NY as well; most companies wouldn't quote for the Tesla Model S at *all*. I only managed to get three quotes, after going to two insurance agents and online.
One of those didn't like my fiancee's driving record and had to "send it to underwriting", offering an absurdly high rate. (She has two collision claims in five years from freakish one-car accidents. The more recent was the high expense of replacing a gas tank which got hit by a ice chunk kicked up by a wheel, developed a hole, and started leaking... an accident which I'm pretty sure would not have even caused an insurance claim in the Model S.) I don't think I want to deal with a company which is that picky.
Geico is surcharging ~$180 for the gas tank accident, but it's still almost exactly $600 / 6 months, which is far better than the competition; the next best quote I got was over $800 / 6 months!
Who's cheapest seems to depend first and foremost on what state you're in. Perhaps the insurance thread should be sorted by state.