It seems like most photography forums are as much about the desire and acquisition of new gear, the next piece of a complete kit, the next part of the collection, etc. Many of the discussions here bemoan the lack of certain types of lenses, no matter how esoteric, for whatever their chosen camera system is, or the camera system they're dreaming about. Let's forget about what's next and focus on what's in your bag now...
What is your favorite lens?
Take that question however you want, but let's keep it to lenses you actually own and use. What piece of glass keeps you in this hobby or profession? What lens pays the bills and is indispensable to your kit? What's the lens you go to when it's all on the line? The first lens on your camera on any given outing, the go-to, the cornerstone, the "if I had to sell everything but one", the glass that keeps you in your camera system?
For me it's my Pentax SMC DA*50-135 f2.8. It's on my camera probably 90-95% of the time. Weddings, landscapes, portraits, chasing the dog, sneaking up on wildlife, portraits of my daughter, doesn't matter this is my go-to lens. It's sharp enough, fast enough, the perfect zoom range for so much, it's images are full of Pentax pixie dust, and it's almost so good that it's cheap for what you get. I love it's rendering. It seriously makes me want to just stay in the Pentax aps-c ecosystem.