I would definitely deal with the title issues first. The longer you wait the more complicated its likely to get.
As for which to work on first, I'd make that judgement more on condition than utility of the vehicles.
Which one looks like you could have it on the road first? That's the one I'd go after. And that decision does include the paperwork aspects.
As for where to start once you've chosen one, there is a school of thought that says brakes first, steering second, then drivetrain third. I like the emphasis on the safety related stuff before having the temptation to drive it.
