18-135 WR vs Tamron 17-50

Now I realize these lenses cover different grounds so comparing them isn't quite exact. But they're the two lenses I'm considering as my first general purpose lens. I plan to pair them up with a 55-300 and a 35mm 2.4.

I don't know what to make of the 18-135, it seems to have a contentious place on this forum. Some early reviews trashed it, people on the forum say that their copy is better than the review indicates, but then other reviews also trashed it. Everyone agrees that the mechanicals are good, but there's a wide variation on opinions about the optics.

The Tamron is the opposite - it's cheaply built and flimsy, but the optics are well regarded, and a 2.8 aperture offers more versatility.

But I also want at least one weather resistant lens - I like to take pictures during rain and storms (and of lightning), so if I end up getting the Tamron 17-50, I may end up having to get the kit 18-55WR lens too for when I need it. So the 18-135 would save me a bit that way.

So mostly I'm wondering - how bad is the 18-135 optically compared to the 17-50?