depends, if you're just starting out with your tgp, use a free one first.
or don't accept submissions just yet. you should focus on trading before investing too much money on scripts, design, etc.
the best free one is
http://tgp.infscripts.com/
it's got all the essential features.
then when you start making money off your site, move to autogallery post.
then if it's still growing and you get more submissions, move on to germesia's brownie script.