Indoors or in darker areas, I use a shade 12 standard glass green lense.  Outdoors, I think a 10 or 11 is plenty.  Plastic tinted lenses are light, but they're sh*t.  You clean them off a few times and they're done.

That's not to say that plain'ol boring glass lenses have their downsides.  Back when I had more of a temper, my helmets flew like you wouldn't believe.  One KA-BAM!  Off the wall, bandsaw or whatever they would hit, and the lense was gone...but then, generally the helmet was done as well!  They're heavier than their plastic counterpart, but the clarity is noticable.

I've used auto tints and gold lenses in the past.  The autotints are nice if you're doing things like handrail or stitch welding.  I'm not really a big fan of the gold lenses.  Sure you can see more colors (purdy!), but a few scratches and they're f*@$&d!  With a gold lense, if you want a shade 10 you'd be better going with an 11.  As far as I could figure, a gold lense was a shade 5 with a plated surface.

The autotint I had was an Optrel.  The lense had a variable lense adjustment (5-12 I think), but I remember it always being darker in the center than on the edges.  Not only that, but godforbid that one has to weld inside a tight space, when BAM!  The sensor is blocked and You get a lovely white blur...

I'm curious though, as to how well an autotint would work in cold weather though.