B-29 for me..
first a walk around, then watch it being refueled and bombs loaded, watch the crew chiefs standing by with fire extinguishers as #3 turned over, then all four engines run up for a mag check while the ground shakes under you, watch it lumber on the transient and turn onto the active... then close your ears as the pilot runs up to MP and roll down the runway.. and hear it for another minute minimum after it rotates and lifts off.
Everything else until the B-36 seems insignificant in comparison (to me)