The class the last needs
TF2 last holds want a medic pair, a pyro on airblast, and someone on the cart. A twelfth sniper on a stalemate last is a meme, not a plan.
Check this resource when a map rotation puts you on a stubborn last.
Uber, spam, and pick classes
Pop uber into space, not into a corner pyro. Soldiers and demos make the space. Spy and sniper punish the people who ignore that space.
Switch class when the hold is already lost. Ego holding scout into a sentry nest wastes the next push.