Is it better to hit the farm or hit the enemie

if by opening you mean as soon as you leave fountain and you see an enemy walking by in the jungle, sure you can give them a quick tap or two but it wont matter too much considering no champion in the game can kill another 1v1 at level 1, and any damage you deal or cooldowns you use will regen by the time laning starts.

if you mean opening as when laning starts, attacking them before minions spawn immediately gives you the lane led via a health advantage. or if you dont have to leash and your stronger at level 1, you can cheese them for the same effect.

Always the enemy.