as above; try both and take your pillion when you try them.
If you're going for 2up riding then i'd say go for the gen1..possibly a wee bit more comfy for the pillion. I mean, look at the pillion pad on that Gen 2!
eeeeh it'd be like sitting on a razor blade
p.s mpg's I cant quite remember what we were getting on my Gen 1 at the time but I know it was very good