Oh, I have such a long post about this, but it's in Hebrew, so I'll recap -
I contacted National more times than I can remember. Their phone reservations center people couldn't give me any definite answers about the length of the contract (i.e. when would we have to check in to renew the contract) and couldn't give me a very attractive price either (even though our rental was a long-term one). I ended up writing to National HQ and they were very nice and basically told me I should contact the local branch directly. So, for over two weeks I tried getting a quote from the sales manager at the National branch in SFO... and he finally came up with a quote which was just as expensive as anything the phone center had given me.
Dollar had a much much cheaper offer. I'm talking a $1500 difference over the three months long rental. I really had hoped National would try to match the offer, but obviously they didn't want our business that badly. I have rented with National in the past and was happy with the service, so had they wanted $200-$300 more, I would have rented with them, but $1500 was just too much.