Still, leves seem better correct? Well, as far as SP goes, yes, but let's say that one day, you have a day off so you can play that entire day!. Let's say you play 1 straight day for...10 hours
Leves: 25-50k.
Grind: 100-150k
Now let's say you have two hours... or more than that. And rather than being a tardface and picking one or the other, your group has this magnificent idea of starting with leves and then griding afterwards!

now you've got 35-75K SP!

But wait, there's more! What if... and I don't know if I should really be saying this here, because it's a trade secret... but what if... you have a linkshell with FIFTEEN MEMBERS who can all party up and do five star linked leves for four straight hours! Considering that you link at most 3 leves at any one point in time... that's an astounding 100-200k SP!

Cripes!