[gregbradley]

Without a doubt the Samyang 14 F2.8. The rest probably all have coma to a greater or lesser degree wide open which does not clean up with camera lens profiles in software. They probably also have excessive false colour which usually is purply/blue halos on bright stars.

Look at all the top images- they are all 14mm F2.8, either Nikon 14-24 or Samyang 14mmm F2.8. The others no doubt are good terrestial lenses but for nightscapes you really don't want to have to stop down to F4 or beyond to get round stars as now you have to use a mount (a Polarie or other). A zoom lens is generally a compromise and usually suffers worse performance than a prime. The Nikon 14-24 is a rare exception. It matches high priced narrower Zeiss primes. It really is the unbeatable lens at the moment for DSLRs.

The first step of any astrophotography is round stars free of coma (comet shaped stars usually in the corners or the left and right sides). That is step one.
Without that accomplished your images will never look that great.

With telescopes that means an accurate mount with nightscapes its means a fast lens that is free from coma wide open. That narrows the field drastically.

The Samyang is probably the cheapest too. I don't know how they do it. The Samyang 24mm F1.4 is also a nice lens. You may need to return a Samyang lens to get a good copy though. There is some variability in quality between copies.

Nikon 14-24 is still the king but its heavy and expensive. You can get adapters for it to fit a Canon camera but no autofocus during day use. Zeiss 15mm F2.8 would probably be awesome too but its $3500!

Voigtlander makes a 12mm and a 15mm but they are F4.5 or F5.6 - too slow.

Fuji makes a superb 14mm F2.8 which is almost the equal of the Nikon but it won't go on a Canon body as they are designed to be closer to the sensor.

Samyang fisheye 8mm is "fun" but gives horrible curvature that does not correct even with supposed fisheye correction software. It does not distort if the lens is looking just slightly above the horizon (this limits the amount of sky you can catch). I just thought - possibly it may work if held in portrait orientation - I'll have to test that. It may also work better using a panorama setup like a Nodal Ninja 4.

Photozone.de is a good resource for checking out lens performances so is DPReview.

Greg.