For me I already have the 25mm F1.4. 20mm is too close.
I would rather go for the 17mm F1.2 if I am looking for a Wide Angle Prime.
I like to shoot super wide, so I am currently also having the Pana Leica 8-18mm.
But on the lookout for the 8-25mm when it is available in the resale market.
The BNIB price is a bit too steep (about S$1699) at the moment.