I assume you mean micro 4/3, not 4/3? 4/3 are different bodies with a different lens mount...
Depends what you use your camera for - just stills or also video?
Both Olympus and Panasonic are due to make new kit announcements next week. Panasonic will announce the GH3 and Olympus will announce a new line of PENs.
The GH3 will be Panasonics top-of-the-line camera, so they'll throw everything they've got at it. The GH2 is regarded as the best videography camera in m4/3 (and better than most dSLRs) so the GH3 is much anticipated. It'll probably be a pretty fine stills camera too, but maybe not up to OM-D standards unless Panasonic have pulled something out of the bag with sensor and processing. The G5 released a couple of months ago suggests they've closed the gap on Olympus - especially with RAW - but are a touch behind and the JPEG engine isn't as respected by many.
The new PENs are likely to feature the OM-D's sensor, but not likely to have the same 5-axis IBIS (it'll probably be a refined version of the old PEN IBIS) or built-in viewfinder.
So if you want the best STILLS camera, you might as well buy an OM-D now as I doubt the GH3 will steal it's crown (although it'll come close).
If you're interested in video, wait a week for the GH3 and see what Panasonic bring to the table.
Olympus have hinted at a "pro" (yuk, hate the term) camera to sit above the OM-D for early 2013, but I would never advise waiting for 'vapourware'...