In general terms, Panasonic had the better motion video features, Olympus had the better stills, but it was / is pretty fuzzy, and a closely matched feature set.
One of my top five favourite blog posts ever is an impassioned rant [1] about digital Full Frame sensors, originally published in 2008 before they became generally affordable (but while they were still very much a fantasy for many photographers who didn't really understand why they wanted one). Updated over the years, and still worth the read.
As someone entering the field without a large collection of (by contemporary standards) poorly designed, overweight, ill-suited lenses -- it was a less complex decision to identify the path that most closely resembled an open standard.
[1] http://www.digitalsecrets.net/secrets/FullFrameWars.html