If you ask me I'm always going to say either stick with 030 for compability or go all out for speed and glory with the 060. There's realy 3 things to concider. Compability, Speed and Heat/Power
Compability: is less with 040/060 than 020/030, and you will at times run into issues with software that wont run on 040/060 but works on 030. The compability is about the same between 040 and 060 but the brand will be a much bigger factor here (stay away from Apollo if you ask me).
Speed: increase from 030/50 to 040/25 is for me is not worth it over the compability issue, however any faster and the speed factor makes up for it. The speed of the 040 is great over the 030 and the speed of the 060 is great over the 040, however we're talking sleek AmigaOS here so the extre CPU speed is not always felt that much... unless we're talking FPU speed where the 060 is miles ahead.
Heat/Power: is an issue with the 040. It is powerhungry and runs hot. In a bigbox Amiga this isn't a big problem but for the smaller A1200 (A500) it can lead to all sorts of stability issues and the 040 will requier a heatsink and likely a fan aswell.
030
- Quite Slow
+ Performance/Cost
+ Compatible
- No FPU
040
+ Quite fast
+ Performance/Cost
- Incompatible (compared to 030)
- Slow builtin FPU
- Runs hot/Powerhungry
060
+ Very fast
- Performance/Cost
- Incompatible (compared to 030)
+ Fast Buitin FPU
+ Runs cool
