I agree. SANEF is the way to go if you are making multiple trips to France. I consider the small annual charge worth every penny and you can sail past what can at times, be quite lengthy queues.
Don.

If you have a card that doesn't charge commission on each transaction in the eurozone (such as SAGA or Nationwide) then that is probably the quickest and costs no more than cash. However some cards are best avoided so use cash - provided you are not travelling at peak times when the queing can be long.
I used to use SANEF liber-t and the bill was paid on my eurozone card but was told than these accounts were being closed for non French residents so I switched to the new SANEF account which is paid by direct debit against my UK bank account. SANEF include a currency trannsaction fee on the monthly account so I now pay more than I used to under the old account

Drive under in the mog.

But seriously it depends very much on your abroad roaming bank charges. I get charged a flat 1 pound every time I use a card abroad. so I have cash in the glove box.

Check out Post Office credit card. No transaction fees abroad.

+1 works for me every time and it is so much fun watching the drivers behind you swerve to another toll booth 'cos they think you are in the wrong lane (especially when in Morgan). In Aero it also meant I did not have to judge invisible wing to kerb ratios and kept in her comfy seat.

Shall be using sanef again in a few weeks time so I am hooked

Not sure if this is true, but I drove a Morgan around France for Mog Mag and we were warned that if you pick up a speeding ticket they clobber you at the toll booth. Never got to find out if it's true but I wouldn't be surprised. Good roads though and very little traffic congestion.

Lived in France for 30+ years - first time time I've heard that...

Or Lloyds although I suspect you may get a less favourable exchange rate.

You can always get a pre paid Visa and load with foreign currency and use that to avoid fees. Works well.

American Express doesn't work well in France, especially for tolls and automatic petrol machines where it doesn't work at all.