Preferred when paying online GBP or €

[deloisy]

I would like to pay an item on Ebay. The seller is in UK. I am in France. The listing is in r GBP. What is the best solution for me

Use my actual preferred currency on my Paypal : €

or 

switch to GBP for this transaction ?

My account is linked to my credit card (France).

Are the Paypal fees and Paypal conversion rate better if I choose to use GBP as preferred currency for this transaction or is it the same  ?

Thank you.