I have owned almost every amiga over the last 20+ years and to me the best is the Amiga 3000 Desktop.
It has the best quality feel of any Amiga. Some of the reasons already mentioned are great ones, here are a few more reasons:
1. The 3000 Keyboards were the best that commodore ever made, Even a 4000 Tower Keyboard, which looks almost identical, doesn't have the same quality mechanism. IMHO, the 3000 keyboards feel the best.
2. The footprint and look of it, I owned a 3000T and I still prefer the Desktop. It seems the right size to me.
3. The metal, buttons, screws, and all the components were a better quality. It feels like quality in using one.
It is a very subjective thing, but to me a decked out 3000D is the perfect package for an Amiga computer.
Lastly, if a user properly cared for a 3000 from the beginning they will last forever. Sadly many 3000's have battery damage. Leaky batteries will hurt a 3000, faster than most any other Amiga because of where the battery is located.
3 Tips for a 3000D owner.
1. Don't let the battery leak.
2. Keep powersupply and vents clean for good airflow.
3. Keep in open area with good cool air. Lifting a 3000 on it's rubber legs will better cool the bottom.