I would suggest 2 warlocks myself.

I'm currently levelling sets of both magi and warlocks and I find the warlocks are a lot easier to maintain high rates of DPS. Certainly with the current balance of classes, warlocks are easier. Corruption + Bane of agony + 2 x demons flies through quests. I play 3 accounts and I find that I can do the equivalent of 'chain pulling' with the ability to do set up lots of dots.

When I am playing affliction, I can target, place 3 dots then change target and I find my demons will finish off any target that I cycle through.

On the other hand, playing the magi is also fun. I've levelled them as frost (you mentioned having pets so I assume you were talking about frost specs) and that is also immensely fun. A lot of frost bolt spam and ice lance of course but overall quite fun.

I have found the locks to churn out consistently higher DPS however and if you were looking at doing any levelling in BGs, locks are your best bet. I find my magi are toast whenever I am locked onto by the enemy team but I can turn a BG single handedly with my DoTS in my locks.Not many FC escorts in WSG can survive each party member with 3 dots on them

Hope that helps