The Pentax is a nice piece of kit, and is good value, but it is a commitment to a lens mount that isn't very popular. If you end up wanting just a couple, and are unlikely to go deep into photography in the future, then it's not an issue and the Pentax is a good choice. If you're going to get into it a bit, then the Olympus (which takes oly or Panasonic u4/3 lenses) or Sony (who makes a ton of glass) will give you more options down the road. If you think you're really, really going to make a hobby out of it then you should get a Nikon or Canon dslr and only spend money on good glass that will last nearly a lifetime. If you want to make it a pathological obsession, buy a film Leica or hasseblad and become an insufferable person who no one likes because you talk only about how you shoot film and how awesome it is and how much of an artist you are.
But really, the OM-d or a6000 is about as good as it gets, and between them it's more about ergonomics and object satisfaction. The a6000 is probably a slightly better camera objectively. The OM-d is what I'd buy for myself because I like dials, and I'm an insufferable film user and the retro styling tugs at my heart.