I hire a car regularly for work, but all UK stuff so probably no use to you. I mostly use reputable companies like Europcar and the like, but for some strange reason easy jet car hire Sent me to Green Motion. It was obviously a tie in as it wasn't obvious on the form where the car was coming from until I paid the bill, and I despite flying into Stansted, I didn't pick the car up at the car hire Village, I was sent to some manky container round the back of an hotel, which just looked like a right dodgy operation. Insurance excess turned out to be in the thousands and even with them taking a 1500 quid deposit on my card, it was still a fortune.
Long story short, stick to the main stream suppliers for both car and insurance and be aware when you sort your own insurance you need to pay upfront and claim back from your own insurers. Potential nightmare