Hit different targets on the BL. After a while you will figure out what's a good amount of money to get from hits for your kcs.
Be aware that there are no "rules" about returning BL hits. Be prepared to be hit back, unloaded on or even noted on. That being said, pvp is a fun part of the game. Good luck!
If by "best reward" you mean the accounts that say "Good Reward" and "Large Reward", definately go for the "Large Reward". But usually the ones that say large reward are bigger than the ones that say good reward. (Because you make more money off of larger players vs smaller players). I hope that helps.
Since op asked for what rewards you get for hitting. You unlock rewards on the amount of successful hits and successful battle defenses as far as I can remember. You need 1300 fight wins to get the max level of the fight awards. Same for dance prank and eavesdrop I guess. Good luck!