Either way is suitable. Lav to Y the stack is the vent for the shower and the lav is the wet vent for the toilet. Lav to T, the stack is the vent for the shower and the toilet and the sink has its own vent.
Great. So just to finish up...the first floor "powder room" venting looks ok? As long as I wet vent the WC with the sink 2" it is ok, correct?