BA: Lots of J-F and a few W-J upgrades (have been Sapphire/Emerald with them for 12yrs). The nicest was when I headed to the airport just after getting a nice Xmas bonus and was looking to pay to upgrade from J to F. The check-in guy seemed confused when I asked about upgrading as the then-wife and I were already assigned in F. Got J-F upgrades on the return flight too.
UA: A short notice longhaul booking all options were hideously expensive so went with UA thanks to free E+ for *A Gold. At check-in the ex-wife and I were upgraded to J. Y-J is always the best.
BD: Was flying shorthaul with my father and we were on separate bookings. He was BD*G and was paged in the lounge and upgraded to C. He turned it down noting he was travelling with me but the agent checked my booking (I was LH*G) and upgraded me too.
My mother seems to be the luckiest with upgrades on BA...flying LHR-DME on a cheap tour ticket booked in Y she was upgraded to WT+ at check-in then to Club World upstairs on the 747 at the gate for both her and her partner. She quite often bags WT+ to CW upgrades on transatlantic flights too.