By far and away the best plectrum for acoustic that I've found is the Wegen bluegrass model (in either 1.0 mm or 1.2 mm).
It's fantastic for strumming, alternate picking, and hybrid picking as well.
These picks are really durable -- a pack of four might last you years if you don't misplace them.
Once they get worn down beyond your preferences a little work with an emery board get's them right back into shape.
If you like a smaller, jazz-style pick for acoustic the Wegen Big City is the best choice in my opinion.
It's fantastic for strumming, alternate picking, and hybrid picking as well.
These picks are really durable -- a pack of four might last you years if you don't misplace them.
Once they get worn down beyond your preferences a little work with an emery board get's them right back into shape.
If you like a smaller, jazz-style pick for acoustic the Wegen Big City is the best choice in my opinion.