Depends on your style....there are panasonic f2.8 zooms, an olympus f2 zoom that no one can afford, or even the tokina 11-16 and primes and adapters. Or you could get the voigtlander and slrmagic primes, which are significantly faster than f2 and can cover your entire focal length range (14-40 is kind of necessary, then beyond that its' a matter of style), but they are expensive. If you love the shallow focus effect you'll have to get the latter.
With the t4i...the 17-55mm f2.8 IS. Easy. And the larger sensor is nice for shallow focus. With the cost of good lenses taken into account, the GH2 is surprisingly expensive, but not worse than the 5D III and with better image quality at normal ISOs.
Getting the best IQ out of the GH2 is a pain. You need to install hacked firmware that can cause overheating and potentially bricking the camera, then transcode your footage using 5D to RGB to retain highlight detail. And the footage still has clipping, skew, and a bit of aliasing maybe...still dSLR footage. But relative to the t4i it's much sharper and with less aliasing. That said, I'm currently intercutting 5DIII footage with Alexa and Epic, and it has similar IQ to the t4i so if you don't mind softness Canon performs okay. But the GH2 remains the best still camera for video from an IQ standpoint. Nothing's perfect, but it is is very, very good.