Here are the kill moves that come to mind (for me):
Usmash - Pretty godly. It has a fantastic vertical hitbox with a sweetspot near the top. Can kill at surprisingly low percentages if used as an anti-air (I killed a Lucina today at 85% with it).
Fsmash - Tennis racket kills the best horizontally. Pan vertically. Gold Club is the weakest but has the furthest range. Depending on stage position, these kill around 110-130.
Fair - One of your more practical kill moves. Kills solidly in the 100+ area depending on the stage position. Slow startup and has a weird autocancel, but it is possible. If you do it while holding a turnip you can cancel all landing lag by hitting down+b when you touch the ground -- very useful.
Dash attack (second hit) - Peach's dash attack is a surprisingly potent kill move, offing lighter characters around 140 and middle weight characters around 155.
Back Throw - With your back to the edge of the stage, your back throw kills around 155.
Honorable mentions:
Parasol - If you manage to hit someone with this off of an uthrow on the top platform of Battlefield or something it can kill at laughably low percentages.
Nair - Good for edge guarding...very fast. Has rather impressive knockback, but I find it get stale for me since this is an amazing approach tool, so I don't usually use it to kill (unless I'm gimping someone).
Bair - Can kill at higher percentages, but has a weird hitbox and its sweetspot can be sort of hard to hit if you aren't right next to them.
Uair - The second hit kills at high percentages depending on how high you are when you hit with it.
