My Tamron 28-75mm f/2.8 pretty much lives on my camera full time, so I guess it's my favorite.
I've found that I use my Sigma 70-200 f/2/8 more from 6-25 feet to really isolate a crappy background for flowers than I ever do for distance stuff. And I use it with a closeup filter for most of the macro stuff I shoot too.
Just started playing with my Sigma 10-20mm, though I doubt it'll displace the Tamron as a fave lens.