For me:

1-Wheels, be they new, trued, tensioned, repacked, whatever. It's what I feel.
2-Crankset/BB. For some reason, I can tell a difference down there. Not sure what, but I notice.

I don't change bars, pedals, stems, frame size.
I don't really care about saddles, wrap, calipers, FD/RD or shifters, as long as they work.
Sometimes, I feel a tire crawl, and it bugs me, but then again, I also think my brakes rub about 50 miles into every ride.

So, in that order: Wheels, then crankset/BB.