The
Canon EF 14mm f/2.8L II is well respected, but quite expensive at $2100. See image quality for yourself at:
https://www.the-digital-picture.com/Reviews/ISO-12233-Sample-Crops.aspx?Lens=454&Camera=453&FLI=0&API=0&LensComp=769&CameraComp=453&SampleComp=0&FLIComp=0&APIComp=0 To my eye, while they are similar in the center wide open the Canon lens appears considerably sharper in the corners than the Rokinon/Samyang (aka Bower, Vivitar, etc.) The difference in the corners is less, but still there when both lenses are stopped down to middle apertures.
Sigma 14mm f/1.8 "Art" also is supposedly quite good (better than the non-Art version that preceded it). Not as expensive as the Canon, though it also isn't cheap at $1600. Keep in mind that the Sigma 14mm Art is an f/1.8 lens... more than a stop faster than the Canon and the fastest available in this focal length. This necessarily makes it one of the largest and heaviest, too. It's about double the weight of the Rokinon/Samyang/Bower. Compare image quality here:
https://www.the-digital-picture.com/Reviews/ISO-12233-Sample-Crops.aspx?Lens=454&Camera=453&FLI=0&API=0&LensComp=769&CameraComp=453&SampleComp=0&FLIComp=0&APIComp=0 To my eye, they appear similar in the center... the Sigma is sharper in the corners when both lenses are wide open... and there's very little difference between them when set to the same middle aperture.
Rokinon/Samyang (Bower, etc.) 14mm f/2.8 are manual focus, manual aperture only.... very affordable at $250-$400 (the more expensive should have a chip that allows Focus Confirmation to work). The primary complaint with this inexpensive version is copy variation.... it's not uncommon for part of the image to be soft, probably a de-centered element/quality control problem. Buyers sometimes have to exchange copies in search of a "good one". Note: This is most likely the same as the original poster's Bower 14mm. The Samyang makes them and sells them under their own name, as well as their Rokinon brand. But they also have been relabeled and sold under many other brand names, including Bower, Vivitar (as a 13mm), ProOptic, and others. Over the years there was at least one revision of this lens, not sure which the OP is using. In the Rokinon brand, the first version was simply labelled "UMC" ("ultra multi-coated", I assume). The later version is labelled "ED IF UMC" ("extra low dispersion, internal focusing, ultra multi-coated", I assume... was the original version not internal focusing?)
Rokinon "AF"/Samyang "AF" 14mm f/2.8.... I think is basically the same as the above lens, but now with autofocus. Relatively new, I don't think this version is being relabeled and sold under other brand names. It has a similar, though not identical optical formula as the above lens, so I'd expect similar IQ. These are selling for between $600 and $700.
Rokinon "SP"/Samyang "XP" 14mm f/2.8... introduced in 2017, this is a more premium build quality manual focus, manual aperture lens with a metal barrel (magnesium), using a different optical formula, and selling for $700 to $800. I also haven't seen this lens selling under other brand names.
Yongnuo "YN" 14mm f/2.8... another relatively new third party lens with autofocus. Don't know much about it. Sells for $500.
The
Tamron 14mm mentioned above was discontinued some years ago... might be able to find it used. At roughly the same time that Tamron was available, Sigma was selling their original 14mm non-Art version.
If considering the above, might also want to look at the
IRIX Firefly 15mm and
Venus/Laowa 15mm lenses, manual focus/manual aperture, both of which sell for around $500. There is also a more robust, metal barrel
Blackstone version of the IRIX selling for close to $700. The two IRIX versions appear to use identical optics.
There also are the premium quality
Zeiss ZE 15mm f/2.8 Distagon ($1800) and [b]ZE 15mm f/2.8 Milvus/b] ($2700), both manual focus with electronic aperture control.
You'll have a tough time finding anyone who has used them all, but can find thorough reviews of many of these lenses at
https://www.the-digital-picture.com/. I find Bryan's reviews very helpful and informative. In particular, check out his review of the original Ziess ZE 15mm Distagon.... which he ended up buying and feels is the sharpest, best corrected of the prime lenses wider than 17mm. He also thinks that the Milvus uses the same optics as the Distagon (which he refers to as the Zeiss 15mm "Classic").
Personally I'd be happy with the Canon
EF 16-35mm f/4L IS USM and plan to purchase that lens when I do my next full frame update. At about $1000, it comes very close to matching the image quality of the much larger, heavier, and twice as expensive
EF 16-35mm f/2.8L "III" (it took Canon three tries to get this lens sharp from corner to corner, but it grew a lot larger too). 16mm is wide enough for me and I really don't need f/2.8 on an ultrawide. If I were shooting astrophotography, I might want f/2.8 for a brighter optical viewfinder.... But tethered/Live View shooting or an electronic viewfinder may make it unnecessary too. The FE 16-35mm f/4L also is one of few ultrawides with Image Stabilization. Also, the 16-35mm f/4 can be fitted with standard 77mm filters (the f/2.8 III uses 82mm).... most (all?) of the above 14 and 15mm lenses have convex front elements that preclude using standard filters. There may be custom filter holders available to allow oversize square filters to be used on them, but those are bulky and difficult to shade very effectively.