All 3 offer a lie-flat bed in J, but only BA has a horizontal bed (QF and CX have a tilt of a few degrees, somewhere between 7 and 9 degrees from horizontal). The QF bed is considerably wider and softer and generally more comfortable (both as a bed and as a seat), but some do not like the slope. So it isn't a simple choice, all 3 airlines have some advantages over the other. You just have to decide how their features fit into your preferences. I would pick QF in J and CX in F as being the most comfortable.