I can't recall a console I sold that I particularly regrets selling, but only because I never really lost out on anything. It's not like I can't still play my favorite games or anything. Also, I eventually reacquired the consoles I sold over time, not particularly out if regret, but out of the desire to share the experience with others in the future.

Though, I did sell a Retron5 that I had, it was the SNES Grey version. While it wasn't exactly a retro console, it was pretty cool being able to consolidate all those retro consoles into one single device, and it looked pretty sleek too. I plan to check out a PolyMega sometime soon, I like their modular console idea a lot.