jumping ship to third party glass.... ??

Okay, I'm just stumbling on this.. I was wondering what you had been up to since you moved. I have Tamron 28-75.... Love it, really.. I notice that you are looking for a shorter focal length.. possible to use for your landscapes? I notice on my Tamron, I'm shooting and the long end most of the time... and the sweet spot is around f5.0.

Can you keep your Canon that goes to 105? I'm always wishing I had a little more length.... Then you can still buy the shorter Tamron and use your current lens to photography your niece at 105mm and get that beautiful background blur...

In my opinion, you generally can't pick a lens based on a brand name. Every maker makes gems and stinkers. Some of Canon's stinkers are the kit, 75-300, 28-90, 28-105, 28-135, and most of their consumer wides to name a few. Once again in my opinion. Sigma also makes some stinkers as well, as well as some lenses that humiliate Canon lenses such as 17-70, 120-300, 50-500, 300-800, 30 f1.4. Same with Tamron, except that their current line up of Di lenses all seem pretty good, except the only stinker in that line up maybe the 11-18. Tokina has it's share of stinkers as well as well as jems.

If you are looking for a particular type of lens (e.g. normal zoom) it's best to look at each brand individually and make your own decision based on optics, build quality, and price. I would never recommend blindly trusting a lens as good based solely on a name.

BTW, with Tamron 28-75's going for around $330, it's probably the best bang for the bucks out there.