BTW, I'm a Tamron fan, and have multiple Tamron lenses I use with my A700.
But, I've seen too many posts about focus errors using some Tamron lenses that should be virtually identical to their Sony equivalents (for example, front focus with some of the Tamron 28-75mm f/2.8 lenses when Sony 28-75mm f/2.8 lenses worked fine on the same camera bodies).
So, I would lean towards the camera manufacturers' lenses when comparing two similar models. The camera manufacturer is usually going to take steps to insure their own lenses work correctly and are optimized for their own camera bodies.
With third party lenses, you're taking your chances on the support available from the third party manufacturer, which is trying to make sure their lenses work with a variety of different camera brands, versus being optimized for a specific camera brand. So, if/when they get it "wrong", a lens may need to go back to the manufacturer for rechipping/recalibration, and you're less likely to have those types of issues with a lens offered by the camera manufacturer.