Years and Years using Europcar and they cannot even fix error message on the Online Booking !!! Better to start using AVIS Car rental ??

Have been using Europcar for Years !!! Now I ma struggling to book a car From Secunda , you book and choose extras then unexpected error message pops up. Have been struggling since February, have been sending mails to so called Managers and still not fixed. After all the years using Europcar do i need to change to AVIS instead ??