IMHO, the 28-2 6 inch is pretty common, and isn't as desirable as the 4 inch version. There are plenty of 6 inch guns out there that languish in LGS and auction sites at low prices.
Having said that, the 4 inch 19-4 with original box, and accessories is not rare, but those that have them , keep them, and don't put them up for sale.
If you like both, but can't decide, buy the 19-4. It is a better "investment" (meaning it is easier to recover, or increase the money you spent).
I live in the "Peoples Republik of Kalifornistan". If that gun came up for sale here, I would be peeling off nine Benjamins so fast they might spontaneously combust!