I have the newer Panasonic on my E-M10 and I am quite enamored with it. It is well-balanced on the camera and quite lightweight. I purposely bought the Pani because of the reviews that I had read and the fact that it has OIS. This gives me the option of using it on Panasonic bodies that don't have in-body stabilization so if I ever move to a GH4, I'll be able to use it with that camera. I would be interested in learning more about the build quality and auto-focus speed of the Tamron. I had a similar e-mount Tamron lens for my Nex-6 and found it less endearing due to the slower auto-focus (it was probably the Nex's fault) and less than stellar IQ which sort of turned me off of superzoom lenses. The Pani has changed my mind about them. It has become my favourite travel lens now when I want to travel light.
I would get Tamron but the price is not right for it, not just now. If it goes down a bit, maybe then. Still depends on reviews, however I saw one and it got 9/10 score.
Only Pana newer version is other choice for me, which is also expensive.
E-M10 + Panny 14-140 II is my most used daytime combo. Great balance and versatility, allowing for shallow DoF at longer FLs. The lens is incredibly sharp throughout the focal range. It is significantly better than Oly 14-150: much sharper, better color and contrast, better handling against bright light (effective coating prevents loss of contrast), much better build quality. I find Power OIS to be equally effective to IBIS at all but very slow shutter speeds where E-M10's IBIS has very obvious advantage. Overall, I prefer using OIS with this lens because LiveView is always stabilized, not just when you half press press the shutter release button. I set E-M10 to I.S. Lens Priority meaning that the choice of IS is controlled via OIS switch on the lens. The lens is also great for macro with clip-on Raynox 150/250 achromat. The build quality is excellent, the exterior is mostly metal except the zoom and focus rings. Silver color is a great match to silver E-M10.
I just got the Tamron and have only taken it out once since getting it. I was pleased with the overall sharpness and contrast of the pictures. I would recommend it especially if you have in camera stabilization.