A1200 is a "usable" machine. You can play games, you can serf the internet (in an "amiga" way...) and of course it supports OS 3.1/3.9.
My advice:
- Buy an A1200
- Some RAM expansion (with or without an extra cpu). If you want to "boost" things up a bit, go for the all-time-classic "Blizzard 1230IV". It will NEVER let you down.
- An IDE-> CF adaptor so you can install a Compact Flash card as a harddrive (fast, little power consumption, almost no "extra temperature"). A 4GB SanDisk UltraII will be ideal.
- Install ClassicWB for AGA (faster than 3.9 - lots and lots "ready to use" pathes and extras - perfect for someone new in the Amiga), also register the WHDLOAD program. It will allow you to install games on the CF card and play them through workbench. No more "insert disk 2..."
- Buy also a CF-PCMCIA adaptor. You can transfer files from your PC to your Amiga with this adaptor. PC must have a Compact Flash reader (really inexpensive...)
With those above you have a pretty neat setup. An A1200 with extra RAM, a small but effective and really non-power consuming "harddrive", a ready-to-use OS and all the games you can ever play, installed on it. A perfect amiga experience of the classic age.