What album have you bought in the most different formats.

I would also mention the best sounding, to me at the time, was the dedicated 4 channel R2R.  
Having seen them in concert on that tour, it captured the moment.  I later abandoned that format due to lack of product.

In retrospect, too many pieces needed, Main amplifier, rear channel amplifier, four speakers and R2R for discrete input as opposed to "mixed" sound for effect.

Probably Donald Fagen, "The Nightfly."  Original vinyl, later the cassette version which I donated to a bar in Kingston, NY.  Then regular CD, then DVD-Audio.

Fleetwood Mac Rumours. 
Original LP
Nautilus half speed digitally remastered 
45 RPM reissue
Original LP White Hot Stamper
CD
The original was of course dubbed to open reel tape and who knows what all else over the years. Its on my iPod, does that count? That would be 7. 

I have several albums in pre-recorded 4 track reel to reel (7-1/2 ips); LP; SACD; CD

1. Original Moody Blues, Go Now,

https://www.discogs.com/The-Moody-Blues-Go-Now-Moody-Blues-1/release/1540468

piano based blues, Mike Pinder's voice, before Justin Hayward. The dynamically played piano on some tracks is muddy on both LP and CD, but sounds terrific on R2R

2. Iron Butterfly, In-A-Gadda-Da-Vida

https://www.discogs.com/sell/item/1142627292?ev=bp_img

on the R2R you can hear 'In the Garden of Eden' here and there

3. Beatles, Sgt Pepper's

https://www.discogs.com/The-Beatles-Sgt-Peppers-Lonely-Hearts-Club-Band/release/9269315

R2R, You hear subtleties in John's voice, Paul's superbly expressive bass playing, things your ears never caught before. My nephew, a musician cried.

4, others of course, I had over 500 R2R, sold 150, been deep into LP last year

now that you mention it, I'm gonna spend some Christmas money on a few R2R if I can find them.

Adventures In Radioland
A & D LP is better but the wide dynamic range makes it hard to listen to. Had to wait 6 years for the CD and SQ not great on the old Rotel.
Current CD Transport much closer.
Electric Dreams good both ways.