A shaped armhole will fit better and have less bulk under the underarm, while a dropped shoulder (when you just got straight up) will fit larger across the arms and have bulk. So, if you're looking for a sleek, fitted look, you want to shape them. If you're looking for relaxed and a bit oversized, go for the dropped shoulder. A shaped armhole can be more restrictive, if the shaping isn't just right. When you raise your arm, it may raise with you if it's too tight. Fortunately, knitting does stretch with you, so it's not as much of a problem as it is with a fabric shirt. But still, it may be a bit restrictive.

Raglan shaping is pretty easy to knit and to seam. It doesn't involve bind off, just decreasing on both sides of the sweater. It looks neater than drop shoulder as well, and is flattering on most everyone.

Hi Dot,
If you are not going to shape, try to be sure and use a nice relaxed yarn. It will fall better. And I would stay away from bulky.
Good luck with the design! I hope you post a picture when you're finished.
Peace...................
Helen