I disagree with the guys saying "try WinUAE first." It's way more fun to mess with the actual hardware.
I went and bought the first Amiga that was for sale near me at a reasonable price, which happened to be an A500+. Played with it for a couple of months, upgraded as much as I could on the budget I'd set for that machine, and then moved on to a 1200. It's definitely the most bang for your buck, original hardware and upgrade-wise. I didn't stop there, though, got a 3000 and a couple of 2000s, as well as a standard 500. All great machines.