So you want to sell a production router and get an end-of-lifed one? Why?

The 2500 is old and outdated. You'd be lucky to find one with IOS 11.1 on it. The 1720 is still doing it's production run (as far as I know) and will have a far more current feature set available to you. As has been said earlier, however, it still won't work with your DSL line. That's the 824 router. Looks like the 1720, slightly different hardware.