If you aren't a very experienced player (and since you are requesting such advise then you probably aren't) I would advise you to stay away from BISHOP. You need to know this game very good and you need to know what to do (how to progress) to achieve resaonable levels on this class. Bishop is considered useless for 95% of random parties and is appreciated only in higher level CP/CLAN play. In duo play he brings almost nothing to the "party" while when planning to join random parties, people simply won't invite you, unless you find some friends who are willing to slow down their progression in order to allow you leach their experience.
If you have a cleric and like healing ppl, simply go for PP. Prophet is still a good semi-healer while being arguably best buffer for most parties. He's great for duo farming and usually there are reasonable ammounts of random parties looking for that class as well.