Hi, I need some info on jogging strollers, specifically double ones (for an infant and toddler). I've seen alot online, and not having children, they're all sounding alike! Which is better...if the front wheel is fixed or swivels?? There are alot of extra accessories...what are "must-haves", what other things should I be looking for?? Anyone with any good brands they like? I'd like to stay below $500. Thanks!