my colleague used http://courier.airasia.com/ to courier his parcel from Penang to Sarawak and he said this the lowest rate he found.

check their website at http://www.gdexpress.com/ la.. haha.

may be can try check with those shop selling piano
see they do provide this service or not
their partner providing service of delivering piano should some how more experience and more trustable

I think all the major courier service provider are reliable
just that are they focus on parcel or document delivery, their pricing, the delivery source and destination, their service to decide whether you chose them.