Tamron makes quite decent glass, and some quite knowledgeable people say their vibration control is as good or better than the big boys' versions. Lens creep can be a bother, if the camera is oriented vertically, but that is true of all superzoom SLR lenses, including Nikkor and Canon. My wife and I have personal experience with pre-VC Tamron 18-200mm lenses on Nikon and Canon cameras. She likes the superzoom concept; I do not. She accepts lens creep and sharpness compromises at each end of the focal range in exchange for not ever having to swap lenses in the field.
True, there is a latch to prevent creep, but it only latches at the 18mm setting.
If you have a Canon, be SURE to buy the right version! Di is for full-frame Canons, Di II is for cropped-frame Canons. Di will fit cropped-frame Canons, but the electronics will not "talk" to each other.
Superzooms are not without merit! My wife can get a shot at a distant bird or something, while I miss some opportunities due to having the wrong lens mounted. On the other hand, I am more likely to have my camera in hand, with a fixed-focal-length 50mm making the whole package handier.
Just to be clear, my wife is much more experienced and talented than I am.
Canon 7D/5D/40D/1D2N; Nikon F6, D700, FM3A, & Coolpix A; Canon 40mm 2.8 STM, 135L, 50L, 35L, 50mm 1.8 I, 100mm 2.8L Macro, 10-22mm EF-S, 28-135 EF, 400mm 5.6L; Nikkor 50mm 1.2 AI-S, 50mm 1.4G, 50mm 1.8D, 16mm 2.8D Fisheye, 180mm 2.8D, 100-300mm 5.6 AI-S, 18mm 2.8D, Voigtlander 90mm f/3.5 SL II