Mage/priest is still the ultimate solo/farming/grinding class. It's extraordinarily versatile. You have powerful aoe's, powerful elite skills and powerful heals. You also get decent burst dps. The thing it lacks is sustainable dps. After an insane 30 second burst (which utilizes many consumables and buffs) your dps drops to very little.
The best way to deal with this is to pick a complimentary third class. My personal pick would be warrior. Warrior supports the mage class well- mage/warrior is easily the best dps mage. Having the ability to triple your dps by changing classes and keeping the same exact gear your mage uses is utility that you just can't beat.
Warmage is probably the second-highest dps class in game, and it's considerably easier to play than it's rival, warden/warrior. While it may seem easy to play on the surface, and it is, there's still plenty to keep you occupied, because aggro management is always an issue. It can actually be pretty exciting having to watch the aggrometer like a hawk and stop/start your rotation and/or even switch weapons to control your aggro. Warmage's always live on the edge, and they frequently die on the edge lol.
Warlock isn't a bad choice however. Wl/m and m/wl are both useful utility classes, and mage/wl (iirc) has a truly amazing party buff that would assure your desirability in a party. Wl/m has a pretty complicated rotation thanks to having to manage your psy. It's not quite as much dps as a m/w, but if you absolutely must have a complicated rotation, it's a good choice. You may end up finding it frustrating though.
Mage/priest is an absolutely ideal class combo to start this game with. You can take that base and build a very versatile and powerful toon. If you have a lot of time to read, check out the Mage forum and read my (immensely) long mage guide, and you'll get an idea of what mage is all about. It was written prior to the addition of the warlock and champion classes, and I haven't updated it due to lack of data, but the comparisons of class combos are still useful, as is the explanation of skills.
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