Hi Roger - you're in for a pretty fun experience ha ha
The long and the short of it is that a 2a and a 3 are pretty similar beasts. The biggest difference is the transmission - a series 3 is full synchro, so you can drive it like a car, whereas the 2a is only half synchro, so you drive it like a garbage truck
Another good reason to get a series 3 is this: It's newer.
All that being said, you may like what a series 2 looks like more - I know I prefer the front end of a series 2, just from a visual standpoint.