Easiest question in the world...Druid Swift Flight Form! Having levelled Brahmin through Outland after the release of Wrath I hit Northrend as soon as I hit 68. This means I never got to use flight form at all other than to return for some herbs and with two other toons with epic flight normal flight form felt painfully slow.
Wizz forward 9 levels and upon hitting 77 I'd managed between all of my toons to accrue just under 7000g. With Brahmin now effectively my main there was never any thought of not getting Swift Flight so off to Dalaran I went for Artisan @ 5000g and Cold Weather @ 1000g; expensive but worth every penny. Whilst epic flight on Daxaar and Nefaros was pretty sweet, Swift is just divine due to the instant cast and ability to herb without switching form.
Those Snowfall Glade Pups for Planning For The Future don't know what hits them when I swoop in every morning. And I apologise to any frustrated player below 77 on the ground when I'm around but hey, I suffered for a couple of weeks at the hands of others.
Of all three toons I now have with Epic flight this is the one for me that truly is EPIC. Rather amusing since it's the only one that doesn't actually share that name.