Between my wife and I, we own a 1st gen mini (silver), a 40GB 4th Gen, and 2 shuffles (1GB and 512MB).
They are all still in everyday use. The mini is the permanent car ipod (Connected to the Alpine Deck), the 4G is the main house iPod, and the shuffles act as both of our on-the-go ipods.
From a design point, I think the mini was the best yet. Aluminum enclosure, first use of the click wheel, compact. Good battery life. Just a solid feeling machine.
From an overall standpoint, I think the current 5G is the best, though I don't own one. Great battery life (for music), thin, brilliant screen, and sharp video. Doesn't get better than that (thus far).
My brother in-law has a nano. It's cool, very small and svelt, but it just doesn't have the tactile quality / ruggedness as the original mini. I kind of wish Apple would be back the mini "mini classic?" in a color screen form, with a 10GB-ish HD. I think it would be a huge seller.
-alywa