MP boost for what? Aren't you changing classes once reach lv30? Then why the heck are you worried about lving whm beyond lv10 right now? And if you want an mp boost.... lv blm damnit!!
If you want to lv something... lv a war. If you really want to be a pali, be aware that without provoke you are useless untill you get the super blind spell.
Even with flash you're super useless. As a paladin you'll most likely be fighting with 1-hand sword + shield with defense enabled meaning you'll be doing squat for damage. Any damage class will be able to out-aggro you, not to mention every single mage class out there.
I had this arguement with someone in my linkshell about which was a better paladin, a pld/whm or a pld/war. He was so certain that a pld/whm was better than a pld/war because more cure = more aggro. However, apparently he forgot about warrior's passive offense/defense up + defender + warcry + provoke not to mention a boost in vitality and strength. Having whm sub would get you more MP + int, but that's not really what a paladin is about. You can spam cures to grab aggro, but a paladin's MP is gimped for a reason. A paladin isn't meant to cure others. It's to throw big self cures and hold aggro. Provoke+Flash+Defender+Sentinel+Cure II, rinse and repeat.
Warrior is actually the greatest class because it's so useful as a subjob for so many of the other classes. Using warrior as a start you can go to Paladin, Ninja, Monk, Ranger, Samurai, Dragoon, Thief and Red Mage. No one ever really wants to see a Warrior with a whitemage sub unless you're using it to play solo.