Honestly........There is no good one!! They all overcharge once you require more than 5 seats, especially when you book late. It's the usual companies + brokers Doyouspain, beneluxcars, holidayauto's etc.
We are driving over with the 7 seater instead of flying as the prices were crazy.....We were quoted between 1,700 - 3k for 4 weeks from the end of July, this was back 4 months ago, so the prices are probably more now. It would be cheaper to hire 2 cars rather than one 7 seater.
Sorry I'm not much help....