Onestar mentored me a while back, before the Great Journey when he was still Onewhisker. Through him I became decent friends with Firestar and Graystripe.
Going by the map, it looks like Shadwoclan territory would be a little quicker, assuming you start at the riverclan camp and end at the thunderclan one. Although, if you travel by night, my territory might be a little safer, because who knows what Shadowclan does at night...... but I'll be watching the border, so I still reccomend going through Shadowclan.