We use the Centuaro Gold Club (3 hirings plus a points scheme that gives discounts or free hirings as we had last trip). The other advantage as a Gold Club member is that they do not take a security deposit if you refuse their 'Additional' Insurance.
Also Centuaro Gold Club members get a FULL/FULL fuel policy.
For the add-ons I have a policy with icarhireinsurance.com which gives 12 months worldwide cover for less than the figure goldcar quote for a few days. If you use this (unless with the Centuaro Gold Club) membership you will still have a security deposit to pay. Google them if you are unsure - my nephew used his global policy in the US to claim and there were no problems at all in doing so. The additional insurance excess for his trip there was $450! so he saved a fortune. the cover is also valid in the UK.