Optimization of Attack Speed / Lifesteal / Attack Damage combination

Three parameters given below and a total value of 100 units may be split at will.

1. Attack Speed (AS)
2. Lifesteal (LS)
3. Attack Damage (AD)

Which combination is the optimal? Imagive a 1 v 1 auto-attack only. ie 25% AS 35% LF and 40% AD? ie 1% AS 1% LF and 98% AD? ie 95% AS 2% LF and 3% AD?

Any math-inside proof? Thanks