Depending on what version of the Tamron 28-300mm you're able to get I'd say go that route, especially if you want to keep a single lens on the camera most of the time (easiest way to keep the sensor and inside dust free). I was able to get the Tamron 28-300mm F/3.5-6.3 XR Di LD (next-to-newest model) for $144 used from KEH. It was their "Bargain" grade (next to lowest grade) and other than one piece of dust under the front gladd I would swear it is brand new. Other than possibly adding a 50mm F/1.8 lens for low light and indoor shooting I'd say the Tamron 28-300mm will stay on my D50 95% of the time.
Some of the older pre-XR and non-IF versions have smaller aperature (F/3.8 instead of F/3.5) and tend to "hunt" a bit more. You can easily identify these as having a large smooth plastic zoom ring instead of the shorter ruberized zoom ring grip (as well as obviously having markings signifying what version).