Originally posted by Polonius Ulf:

The SoE generates more XP per hit, but has a much lower rate of fire. The staff of frost can rapidly generate multiple hits with a single activation. So it is not true that the SoF is worse for skilling-up than that the SoE. They are about the same.

Each of them also need some player skill. With the staff of frost, you want to learn how to dish out just enough hits to do the job and conserve eitr. Another player skill is dealing with multiple foes by freezing each of them with just a touch of frost. "I'll get back to you later." With the staff of embers, you have to both lead and loft your shots to score hits.

It's not just about the rate of fire, in fact, the rate of fire is what makes the Skill up on the Staff of Embers faster. There's a brief window between casts where you will actually regenerate some Eitr, This means for a full manadump (~180 Eitr) the Staff of Embers produces 25% to 50% more elemental XP per bar.

There's also the overkill factor. It's not really possible to overkill with the Staff of Frost, but a hit on a mob with 1% health still gives full XP, so it's XP per hit advantage really starts to pay dividends while leveling it up, especially on trash that the Staff of Frost will just as likely kill in one hit as well.