Do any quest that fits your play style. If you're grinding on X monster, then it
may be a good idea to get a quest that is on that monster. I always had enough SP even though I quested, but that is because I usually have gaps between and around 3-5.
Silkroad can get really boring, but quests like Ceberus, Ivy, that one where you fight the huns produces nice entertainment. But generally people don't do those sort of quests, which is depressing (

). Silkroad, always about the grinding and trying to achieve that fastest level-up.