Been through my fair share of em. I still have my 12mm fisheye. I'll be trying the GM out for awhile but the canons are up for sale without interest and for now it's just a debate between the GM and the 12-24.
I wanted to do some testing too.
Go back 5-8 years ago and I was shooting constantly at 17mm on the 5D2 as my 'wide' - my others were 50/1.4 & 135L
Now, the widest lens in the past 5 years has been 28mm......








