Between the two lenses the I think your only choice is the Tamron. With the kit lens you currently have 17mm and f3.5 so the 17-40L will be worse in low light. Its a sharper lens but indoors your probably wont have the light and will end up losing sharpness by increasing the ISO. The Tamron will give you an extra stop over the 17-40 which will double your shutter speed.
If you want more light, the Samyang 24mm F1.4 could be an option, its reasonably wide and very fast but its one focal length and manual focus only. I have the 35mm and its a great lens.
What’s the main limit to using the kit lens? Low light conditions?
Thankyou.
I’ve decided to go with neither of these lenses, and instead to go with the Sigma 18-35mm f/1.8 and just hope that I don’t upgrade to a full frame anytime soon. Everything I’ve heard about this lens so far has been good.
Also the kit lens just isn’t a great lens. Focusing is slow and loud, and image quality isn’t even close to other lenses I’ve used.