It is a subjective choice. I try to avoid duplicate rigs due to space limits. 86Box, PIII (Win98), Athlon64 (WinXP), PhenomII X4 (Win7) fills a very long period without much overlap.
I happened to focus on rigs I never owned. I had a Pentium MMX, K6-2, Athlon, Athlon XP, Core 2 Duo, Core 2 Quad so I'm not interested in that.
Pentium III 900E, ECS P6BXT-A+, 384MB RAM, GeForce FX 5600 128MB, Voodoo 2 12MB, Yamaha SM718 ISA
Athlon 64 3400+, Gigabyte GA-K8NE, 2GB RAM, GeForce 9800GT 512MB, Sound Blaster Audigy 2 ZS
Phenom II X6 1100, Asus 990FX, 32GB RAM, GeForce RTX 2080 Ti