If you're looking towards endgame raiding I would say go with either a box combo with a mage or just play something else altogether. You generally will not see more than one in a raid, and all guilds that I'm aware of raiding already have one. Wizards, and druids generally tend to have multiple copies on a raid, so you're safer with one of those.
Speaking from alot of experience in this area your main attractant to groups at the high end is generally taken care of by bots, or bumming summons off of mages, so I wouldn't expect to get groups off of that. Your best bet to getting a group at any level is to simply make alot of friends. Rogues, rangers and wizards all never pretty much stop doing dps (melee, melee+bow, and 5m nukes) so you lose out alot on that.
The differences in pets seems like it might be really great, and it is soloing at earlier levels, there are some basic assumptions you should hold however.
1) You will probably never use the earthpet in a group. Ever.
2) You will use it heavily up til the point where you get earthsplit at lvl 61.
3) Air or waterpet will be used 90% of the time. Firepet has the lowest hps, and 90% of the time you can expect none of the healers to pay attention to your pet. Unless of course its someone you work with really frequently, and even in that scenario, they tend to forget alot. So it becomes a pain in the ass. Once you get the recall aa and max it your pet will die much much less. It is mad crazy handy.
As far as aa's go, you'd want to acquire the crit aa's, host of the elements, frenzied burnout, elemental barrier (if you are raiding muchly), elemental mastery, and enhancement, lr5, up5, hastenened mending and mend companion, and recall minion for starters. Mages top out on aa's very far in, so expect a tremendous amount of grinding to max. As far as the elemental form aa's go, earth is pretty much pointless if you ever intend to get dragon/giant bp clicky, fire is good early on b/c it helps you max your int more easily and quickly. Air is the form of choice for raiding, providing a buttload of resists at each rank. Water is the other alternate in addition to fire. Handy soloing b/c of the hp regen, and an acceptable alternative to fireform.
Rain Rain Rain. You will do this alot. I wouldn't pay attention to your single target nukes at all for the most part. Just learn to gauge distance and you should be okish for mezzed mobs etc. The only time you should use single target nukes is really if theres and unacceptable amount of distance between your target and a mezzed mob, or if your target is very mr. Then I would suggest a firenuke, probably scars of sigil (55 iirc). Also if you are a mage, you will love that spell much. It never goes out of style. Given a choice between the archaic and relic nuke both up, or sigil up along with one of them, I'll always choose sigil.
And yes, back before the nuke changes, druids were 2nd best, after they were still 2nd best, after rollback, they are still 2nd best, unless magenukes have been modded again.
They are very fun to play, but expect to get pretty frustrated down the line.