The dreamstate vs intensity battle is long ranging and you actually have to look at it from a different perspective than just "Is X > Y or is Y > X."
In general most people and general logic will lead you to believe that as a boomkin intensity is better than dreamstate. In most cases this is true but there does become a point with how the gear scales that dreamstate could overtake intensity in the actual regen.
Case in point.
Right now blizzards boomkin itemization and class homogenization has been pushing more and more spirit upon our gear that we wear. More spirit obviously will lean you towards intensity as its spirit based regen. So if you actually have gear that has more spirit than it does intellect logic says take up points in intensity for the extra regen.
Now if you're going to be fickle about it, I know I am, you'll be picking up items with no spirit and has more "tri-stat" orientation. Items like the ring, Signet of Manifested Pain off of KT with haste/crit/sp/int and stam. With the lack of spirit you'll have more desire to use dreamstate.
I wish I could give you a definate answer on the question but since I'm not the best with math and I don't know the actual spirit to mp5 conversion I won't try to give you misinformation.
So, here is what I can tell you to try so you can figure out the best form of mana regeneration for you.
Go to a target dummy, something you can hit just to be safe. You cannot be spec'd into Nature's Grace at all because this will actually affect your testing and try either 3/3 Dreamstate or 3/3 Intensity. Stay in caster form you want 0 chance of crits having any effect on your mp5 with mana returns from moonkin form. Make sure you have recount set to current fight so you can determine the length of the fight before you've officially been run oom.
Spam wrath until you're oom. Record your time until oom. Rinse and Repeat a few times so you're not limiting yourself to just one variable to test.
Respec into the other mana regen talent you have. Do the exact same thing. This will give you a better idea of whats better for you.
But all in all if you don't really care, both of them actually give you more mana regen and that I guess is the ultimate goal you're going for. So all in all you could just pick one that you think is better.
Do the same thing