HELP:EFS TY OR GREENFIELD OLYMPIC

My daughter is now attending PN @ Greenfield, we are really happy with the school, however we are also getting an offer from EFS Tsing Yi which is closer to where we live. We are planning to send her to int'l school in the future, but also do not want her to lose her Chinese ( mandarin) skill. Shall I stay with greenfield with bilingual( English n Mandarin) or EFS with English only?
In terms of the curriculum, which one is harder?

Please help!