Rachie,
The basic pay differs between airlines but most charter carriers work out the same in the end, Britannias flight pay is higher than MYT so you will earn the same roughly at MYT and BY at the end of the month, if i was you i'd take BY. The longhauls not as good now at MYT not like the old Airtours days and chances of being kept on are low. Good luck anyway and happy flying.