If you need AF on the GH2, then you are pretty much looking at the offerings from Olympus and Panasonic.

The newer lenses generally have improved AF speed, so I would keep that in mind when you do your shopping.

The most important thing is to determine which focal range is going to be most useful to you before you get start looking: Do you primarily need wide angle to standard? Or is standard to telephoto more useful?

You'll still have lots of use for your primes because the AF zooms don't open up as wide so they all have disadvantages for lowlight.

The Panasonic f/2.8 X series lenses will work better than most in lowlight situations... and the price reflects that.

If you can deal with less in the way of lowlight performance, I would read the reviews on the "LUMIX G X VARIO PZ 45-175mm / F4.0-5.6 ASPH. Lens", "LUMIX G X VARIO PZ 14-42mm / F3.5-5.6 ASPH. / POWER O.I.S. Lens". They are all servo zooms for a lot less.

The Panasonic 7-14mm m43 is a specialty lens not generally suited to unpredictable work. But if you really need to go wide, it's one of the widest out there. It's also not cheap.

You can get a sense for many of the lenses available at this link (I changed the parameters to mirrorless lenses from Panasonic and Olympus so it should all be 4/3s or Micro 4/3s lenses).

http://www.bhphotovideo.com/c/search?ipp=100&Ns=p_PRICE_2%7c0&ci=17912&N=4196380428+4099560890+4099560888+4099560884+4291296566+4291306223&srtclk=sort

Just to point out...Olympus lenses will not have OIS and they may matter if your camera body is Panasonic. Some Panny lenses do not have OIS as well. Especially at tele range, OIS will be really useful, more so for stills.