That is simply a too open of a question.
Check out Theo Waynne's sight, where he explaines the difference in mouthpieces compared to what you want to produce as a sound, or should I say, the sound you are trying to emulate.
You need to have some idea what sound you like and are trying to emulate. Who are your heros on the horn. Whos sound do you like? Your post seems like that never entered your mind.
For me, all my Heroes play on an Otto Link.
Coleman Hawkins, Ben Webster, John Coltrane, Johnny Griffin, Eddie Lock Jaw Davis, and my friend, Lew Tabackin
I have stuck with Links, even though there are many options out there.
As an example, on everyday playing, I have a piece that after many years of searching, seems to be the piece for me.
BUT, when I play classical music in a classical quartet, or the rare occasions that I would solo on a classical piece, I revert to an R Caravan. This piece is more inclined to give you a correct dark classical sound. Like Adolph Sax expected.
But, any known player has his own Chops. No matter what mouthpiece a seasoned player plays on, he or she will still sound like themselves. To quote Doc Tenney, "You can't buy Chops in a Box". It truly comes down to your own personal choice. If you dont know who Paul Doc Tenney is, look that up also.
Ironically, Just Yesterday, I pulled out my collection of 8 treasured pieces, I have in my collection. I decided long ago, If I am going to collect vintage Otto Links, I will stick with 8 and have to sell one in order to get another. After playing on all 8 yesterday, I jumped onto eBay and ended an auction I had listed, because I realized a piece I was selling was just better than I had remembered.
You probably need to step up from what the horn came with, but you still don't seem to know what your desired sound would be. Thats the personal choice only you can make.