Monona Terrace (DOWNTOWN on the study map) was the planned station location for the ill-fated (and poorly marketed) 2008 Madison-Milwaukee train line. It would be a great location for people getting on or off the train in Madison. But because of the backup move required, I don't think it is the best location for through trains.
It seems most likely that the Monona Terrace will be chosen again, with the Madison Airport location being the next most likely.
Best case scenario IMO:
- Monona Terrace downtown station now
- Madison Airport station later, when they re-route the Milwaukee-MSP trains through Madison
- Madison builds good transit (BRT, streetcar, etc) between Madison Airport and downtown
- Trains that end or begin in Madison use Monona Terrace
- Through trains use Madison Airport