I mostly fly AA,BA and AY. Why I don't want to stay on AY is because I get less points from them and then their taxes are way higher than anyone's else.
AY
real taxes are exactly the same as for all other airlines on the same route & class of travel.
Co pay fees & surcharges differ betweeen airlines.
Do not confuse real taxes with airlines imposed fees (~profit)
In times past BA flights got nil/less AA miles, but now is as the link above. Always check the fare bucket you have bought
Points/miles are not equal between airline FFP's. Its all about earn/burn and what your objectives are from a FFP