Dear Peter, 

If you become a diocesan priest there will be a lot of work for you to do, you will serve Christ well and you will do much good. If you become a religious priest the same is true. 

If you look around you and see all the needs there are you will also immediately realize that there is no way you can do everything, respond to every need and solve every problem. It may be frustrating but it is true that in order to do the good that God is calling you to, you will always have to leave much more undone. That is how limited we are as humans! The most we can aspire to do is the little bit (and it really is tiny) that God wants from us, and with our prayer and sacrifice in union with Christ make the effect of our little and poor work infinite through association with him. 

So the question to ask yourself is, Where does God want me to be? Try to see what are the needs that touch your heart the most - this is one of the ways he has of telling you what he would like you to do, what part of his vineyard has he called you to. Try to see where it is that you experience, "this is where I was made for, this is home" - not that it is going to be easy. Do not mistake thinking something is going to be easy (no vocation is, not even marriage) with where you were meant to be. 

So if you don't already have a good idea of where God wants you to be, go visit your two options. Speak to the people in charge in each place, meet the seminarians, spend time in prayer, live their life a little, and see where you are more "at home", where the thirst that God has placed in your soul finds satisfaction. And again, both ways of life, the diocesan and religious priesthood, are going to mean great sacrifice and enormous generosity if you are going to do it right. 

God bless.