I have basically all Amigas. Knowing that here are my recommendations:
1. Play with emulation first, get familiar with it.
2. If you can afford it and want real hardware there are 2 options: A500 for classic experience, A1200 for best experience.
3. I'm not sure if you want productivity or games on Amiga, if you want it for mostly games, maybe try Amiga Mini.
In my opinion, if I had to sell all of my Amigas and ONLY keep one, I'll pick A1200.