Ada 1 - 45 Ada 2 - 30 Ada 3 - 40 Ada 4 - 15 Ada 5 - 40
In Leon 1, you can start in The Town and get all the kills you need. For Leon 2, you can start in the Underground Lab, but be sure to kill all the enemies that appear in the area with the chute before you jump down it (they DO stop coming), as well as all enemies in the lab proper (be sure to open all the doors). Leon 3 and 4 need to be started from the beginning. Leon 5 can be started from the High-Rise Area, skipping the annoying beginning.
Chris 2 can be started from In Front of City Hall, but be sure to kill as many J'avo as you can in this area. You also should play it safe by killing all enemies in City Hall, including the Napads in the foyer.
In Jake 2, you can skip the blizzard part and just start in Snow-Covered Mountain. Likewise, you can skip the beginning of Jake 3 and start in the Living Quarters. For Jake 4, the Shopping District (4-4) will work, as will the Lower Levels for Jake 5.