I'm currently dualboxing a druid and a mage.

I chose to make the druid boomkin and play it as my main character and went with frost on the mage. I wanted to create a team that took care of business before they reached the duo and if they did the main character would be able to soak up some damage.

Since I wanted to be sure that the druid would be able to be the ones who gained most agro I didn’t pick any talents that reduced it on the druid. And since the druid ended up to be the main character I focus more on that castingbar, which optimizes the casingsequences and gains more agro. I find that the mage rarely pulls agro.

Good things about a Boomkin and a Frostmage duo.
+ Slows things down and you can kill things before the get close to you
+ Ability to freeze things and backup
+ They can crowd control two different targets and take care of a couple of others
+ Trees and Water Elementals at bad pulls
+ Good use of buffs and auras
+ Good dps
+ Portals
+ Free food and water

Bad things about a Boomkin and a Frostmage duo.
- Ability to heal the druid when it has agro
- Not using the mage to its full potential since it is used as a sidekick
- Both characters are looking for same sort of gear

I really enjoy playing that combination and don’t think I would have done it any other way if I would have had to redo it all again.

Well that is how I do it, what you do is totally up to yourself… I would suggest that you pick the combination you think you will have the most fun with. Good luck!