The best experience comes from constantly grinding. Yeah, 4 energy for 30 xp over 9hr equals about 3.33 exp an hour. If you spent all your energy on a all the long bakes that will equal 180xp.

If you were to drain your energy at once (at 3 energy for 10 xp) you'd get 70xp off the initial grind. Then, considering it takes 5 minutes to regen 1 energy point. You'd could run 4 instances an hour which would equal 40 points per hour. Over a 9 hour period that would be 360xp. Keep in mind this isn't including xp bonus when grind, which you get a fare amount of. The total altogether would be about 430 xp in the instance you didn't get once energy bonus drop.

Of course the best solution would be to slow bake your energy and grind off regen, would equal 610 xp.

In any case, just always make sure your energy bar isn't coasting at 25/25. It takes 2 hours for the bar to go from zero to full. Thus, you wanna make sure you're dumping those points into what ever, every two hours.