I'd recommend the 10". Having owned 8, 10 and 12" solid tube dobs I think the 10" is the best all-rounder. But the 8" is a lot more mobile. Take it to parties move it around easily from back yard to front up and down stairs in and around, and sometimes even by, intoxicated folk. Couldn't do that with the 10", which for my personal use is the best though.
If you look after the scope you can expect to sell it for between 2/3 and 3/4 of what the cheapest price around is at the time.
One quickly gets used to manual tracking with the Dob mount. It's rarely an issue with deep sky objects which are viewed at low to medium powers. Takes a little practice with planets at high power but it becomes second nature after a while. When I look through a tracking scope (of which I own one) it feels like there is something wrong with objects just sitting there motionless in the FOV.
