I prefer Thursday, but there is rationale for all days and I agree it's subjective. I think you should chose whichever day you prefer and fits with your clinic schedule.
I find that Fri afternoon med onc/infusion centers can be sparsely staffed, so if a patient is borderline between admission or just needs labs/fluids, then Thurs afternoon is more amenable to checking labs and getting them fluids rather than Fri afternoon. In addition, if you miss them on Thurs you can see them on Fri.