[Rover]

Had the Sigma 20mm f1.8 a great lens (soft at f1.8 however) and I regret selling.

This one seemed to me the way to go until I saw the picture: Why this protruding front element ??? We need polarizers at 20mm, plus thr protruding front element on the Signa 14mm f2.8 created me tremedeous  problems, disppointed...

"Great lens but soft at f1.8" - well, to me it killed any appeal of this lens; what's the point in having a f/1.8 lens if you have to use it at f/4 or so...

I'm also a user of Sigma 14/2.8 and while the bulbous front element is inconvenient, it's not a deal breaker in my opinion. The 20/1.4 has a much less curved glass in front it seems, more similar to a Canon 15/2.8 fisheye of yore.

By the way, on a Sigma 14/2.8 you can also use gel filters in a pinch - though I never bothered to try them.