Nostalgia and collecting are different things.
For Nostalgia, it’s any Amiga you have a fond memory of using.
For collecting, it’s a boxed Amiga 1000 system, since the original of any platform is generally the most desirable.
The 500 could also be considered collectable, as it goes right along with the Atari ST and the C64 as one of the most influential home computer game consoles of all time.
Other Amigas can be very desirable to collectors based on their condition and their relative rarity. For example, An NTSC Amiga 600 complete in box is surprisingly rare in the US, but a PAL 600 complete in box is common. The 3000UX and the Commodore-Amiga 4000T are also rare.
There’s no real set value range for any Amiga, despite eBay auctions. The 4000 is still generally the most expensive, since it’s still used as a daily PC. In 15 more years, we’ll have a much better idea about which Amigas are hard to find (and fetch top dollar from collectors.)
As I think I alluded to in another thread, sometimes it’s the add-ons that are most desired by collectors. I paid more for my circa 1985 Los-Gatos Amiga “boing” logo plate (the badge that is affixed to the 1080 monitor’s bezel) than I did for a circa 1985 new-in-box 1080 monitor