Had the samyang 14mm/2.8 which is decent lens of you manage to find a good copy but with HUGE distortion. It's also a DSLR lens i.e. huge.
The sigma ART 20mm is also a DSLR design that's rather big. But from what I have read it's sharp.
Used to own the voigtlander 15mm f4.5 which is a small and sharp lens that makes beautiful sunstars from wide open. Get this lens if you want ultimate portability with great IQ. The down side is the good is fixed which means you can only use 58mm filters i.e. no step up rings or square filters which can be a hindrance for landscapes.
I currently own and shoot with the laowa 15mm f2. It's fairly small for such a fast lens. Very sharp even from wide open. Beautifully designed and best of all it takes 72mm filters with a hood that comes off.
I hear tokina firin is decent but never really used one or tested one to comment.
Other options:
@stevelmx5 was selling a Nikon 20mm f3.5 which is very decent and small.
I used to own a Olympus OM 21mm f3.5 which was sharp and small.
Zeiss Batis 18mm f2.8 is one of the best UWA money can buy.
There was a couple of Sony 16-35mm f4 lenses in sales forum. A great sharp lens with a very useful zoom range.
I recently had the tamron adaptall 17mm f3.5 and a tokina 17mm f3.5. they did well stopped down to f8-11. They are cheaper but you get what you pay for with these.
I am bit of a UWA junkie
I have basically owned or used a lot of them, more than I care to remember lol