David,

For rough seas or outings in which I anticipate rolling my Shearwater 16, I use the Seals "Extreme Tour" size 1.4.  I think some retailers may also list this same sprayskirt as the "Sea Tour Extreme".

For more relaxed flatwater paddling (and hot weather), I use the Seals "Mariner", also size 1.4. I've found this skirt to perform well when rolling, but nothing beats the heavy-duty reinforced neoprene skirts for rough conditions and frequent immersions, which is why I think the "Extreme Tour" beats out the Mariner if you are planning on focusing on rolling practice. 

-Mike Torres 

Hmm...  I wish I had ended with "...if you plan to focus on rolling."  I guess reading the forum and replying at midnight makes clear thinking and writing more of a challenge :-)

I use the NRS Catalina for my Shearwater. Water doesn't pool with this one, one of my favorite features.