I'd try them out in a store. The A230 is designed to be very beginner friendly with a nice menu system to help you understand how settings are going to impact your shots.
The 20D is a larger and heavier camera. But, it's in a more advanced market niche, and it's got a larger viewfinder, better build quality, more advanced control layout, and faster burst speed in continuous drive mode. It's 8 Megapixel Sensor is also pretty good.
But, it is a 5 year old camera, so I'd be concerned about reliability, depending on how it's been used (not to mention that things like internal capacitors can break down over time). Of course, a 6 month warranty would help with peace of mind if something went wrong.