I'm currently leveling up four 5-man party. One party at a time. I found that for me, just having five-man parties of well-geared characters running through level-appropriate dungeons is the way to go. They're currently all in the 30's. Each party has a tank, a healer, and three AoE dps chars. All of them are Tailors/LWers/Blacksmiths for self-crafted gear and Engineers for extra damage with bombs.