Veneer or Crown for Calcified Tooth?

If discoloration is the issue, I would use a porcelain veneer to correct the aesthetic concern.  This would be much more conservative that a full crown.  In addition, should the tooth ever "flare" up and need a root canal the could do it from the inside of the tooth without affecting your porcelain veneer. 

Since a veneer is a more conservative treatment for the tooth (I don't have to grind the tooth down very much), I will typically use a veneer in your case - as long as the tooth is otherwise intact, healthy, and has no other large restorations. To be honest, in cases like yours I will often veneer both front teeth with extremely conservative veneers (even no-prep veneers should the case allow), so that the two front teeth will be made out of the same material -- if I do only the one front tooth, I will have several try-in appointments so that I can tweak the porcelain until I get it as close a match as possible to the neighbor tooth. If you choose to do just one, it costs the same as two due to the greater number of appointments needed to get it just right.

I see this frequently. In my hands a direct resin veneer (bonding) is the best way to handle this situation. I have total control over the shade, shape and form. Darkness can be dealt with. It's immediate and it does not involve an off-site lab. It's simple and straightforward to match the adjacent teeth exactly. The shade transitions, nuances and translucencies can all be designed in. It only involves one tooth and it's the least invasive. Properly done direct resin veneers are a superior restoration.