I've tried many of the prime lenses, and the best I have found is the Zeiss Distagon 15mm f/2.8. It is very expensive at $3000. I can only afford to rent it, but the micro-contrast and color is just amazing. It's hard to explain how good the RAW images look with this lens. I've never seen anything like it. Yes, the Samyang is significantly cheaper, but I would be willing to bet it doesn't even come close to the "look" of the Zeiss glass.
For meteor photography, I stop the Canon 14mm f/2.8L down to f/4.0. There is still a lot of aberrations in the corners. I've come to accept that fact.
I stop the Canon 24mm f/1.4L down to f/2.8 with just minor aberrations in the corners. I sure hope Canon's updates improve their coma problem; however, I would be surprised if they do. I'm looking forward to seeing what Zeiss puts out in their Otus line. I'd be willing to spend $4000 on a lens that has excellent stars stopped down to f/2.0 or so, especially if it is 21mm or 24mm focal length. That would be a dream.
I have included a few non-cropped examples.
You can always rent the Zeiss lens. The only downside to renting the Zeiss lens is you'll want to buy one afterwards.