I don't know if this has been linked before, but here is a great analysis and insightful explanation of the 'restoration' of Dumbo for the 60th and 70th Anniversary: http://colorfulanimationexpressions.blogspot.com/2010/05/dumbo-for-our-times.html
In light of it, I'm currently leaning towards the in-between "Big Top Edition" release. It might lack a bit of vibrancy you'd expect, but it just might be the least messed with. I'm having trouble making that firm, since I can find few comparison screenshots.
Also, not certain yet, and this is a crazy weekend for me so I'm doing as little as possible right now, but I'm seriously considering removing any Diamond Edition recommendations for films older than 15-20 years. Disney seems determined to make all their films look no older.
That'll roll back the Bambi recommendation :
Platinum:

Diamond:

I don't know if what we see there is aging, film artifacts or brush strokes, but I do know I see lines disappearing. The Diamond looks better in theory, but the more we learn about the Diamond series, the less benefit of doubt I'm giving them.
I'll probably back off the Alice in Wonderland Diamond recommendation as well.
Finally, knowing a bit more about things, I'm thinking of reinstating my Little Mermaid preservation as first choice. (The Dumbo article above does mention that early DVDs had the contrast pushed. Between that, the test screenshot I made above, and poita's vblur comment, I have to think the Platinum isn't as awful as we first thought. We'll have to wait for the Diamond edition to have something to really despise.
Comments? Dissension? Those in favor?
Btw, it appears for the moment Cinderella non-Lowry has a seed.