ASE's aren't a priority in my life, but when I consult my gut on which way I'd go if they were, I'd do Proofs. Crown-size Proofs are something not possible in the rest of numismatics due to their huge size; nothing else like mirror fields literally large enough to shave in. "Business Strike" ASE's are - to me (and the Mint) - simply large lumps of silver whose purpose is to park money in precious metal. I'd do them in a CAPS-style album, or something similar using Airtites to insulate them from the atmosphere for good.
I agree the proofs are beautiful. But, there is nothing to stop me from going after them once I am done with a BU set. The haze and spotting issue just really worries me...and I remember that being a big problem with them.
I have a Dansco for my bullion ASE's. I also have both graded and ungraded proofs, but only one or two of the early dates show a small amount of hazing. Good luck with your choice. IMO, the proofs look like jewelry, so I keep them in airtite containers to minimize contact with the elements. That's just me.
Outside of the hazing...do the proofs tend to me more reactive to toning? In my head...it would be the opposite. The proofs have a smoother surface and therefore any oxidation layer would need to be thicker before it starts to affect the surface and refract light through it. But, it might be backwards in that thinking.
I'm not sure about the toning. I'm more concerned about marring the surface with unnecessary contact.
Fair enough. Although it's a risk with either...it would be more detracting to eye appeal with the proofs for sure.