Pick the same classes you enjoy in vidya RPGs and might enjoy roleplaying as? RP'ing should be a much larger aspect of a campaign than in video games. So you might want think about the type of personality/background/etc that sounds fun to play to you.

DnD can be a lot of different things, but in my experience it works out to be a combination of this joint effort by the forum, and numbers based combat/interaction/exploration/skill development.

Since this is a short, single-shot campaign, it might work out to be a lot more combat focused than normal. That's not how it has to be. It could be largely a puzzle, or something more based on the social aspect of people-problem solving.

If you're new, picking a magic user class or other classes with several different resources to keep track of may feel tedious or over-whelming. There's more paperwork to keep track of. A more straight forward class like fighter or barbarian might be good to get your feet wet with. Don't let that scare you away if you really want to try another class though. It all flows together well once you familiarize yourself with it.

EDIT: Also, barbarian and rogue make good partners. Del and Jinx should have fun working together with a little coordination/communication.