Hi there Jan! I don't want this to sound like a cop out - but partly it depends on your design. Obviously thinner walled is going to be much easier to flare and bend over. I always buy seamless. Two reasons - 1. it will look cleaner and 2. I'd worry about the seam splitting with all the pressure.

I mostly use something that is about 9 gauge with a 26 gauge wall. Like this:http://www.thunderbirdsupply.com/proddetail.aspx?stockNum=110142

I have never used fine silver tubing and I think it would be perfectly fine for short rivets - for example, covering a drilled hole. It may be a bit too soft for using as a long rivet - either telescoping or attaching a bead as it may have a tendency to bend in the middle as you work it.

What is considered a 'large' size ? (the ones Rio has?)