My recomendations go against a subway (which is unbeareably slow) and not compatible with both games in general and some tcp-ip stack.
I would buy either a wifi or ethernet pcmcia card and conect it to your PC/Mac home desktop. In this way you will get fast transfers from one to the other with minimum trouble, avoiding removable parts (CF or SD cards).
Dont go for the FastATA adapter, it is really meant for high end systems, not for a gaming rig. It will eat nearly all your precious cpu cycles.
In my opinion, unless you are into the souped up A500 experience, which involves expensively upgrading your A500 system to the extreme, and running serious applications, I find there are plenty 16bit scandoublers much cheaper than the Indivision ECS.
For your Amiga 1200 there are cheaper scandoubling solutions, not so full feature though, but then there is no Indivision 1200 on sale.
So I would buy a PCMCIA ethernet or wifi (whichever suits you most)
and buy another scandoubling solution (70 USD if you know where to dig)
