iplayer on the Playbook doesn't offer me the opportunity to download.
In any case, unless you want loads of local storage and/or an HDMI output, I'd go for the Nexus. There are limited apps available on the playbook, and most of those that are available are more expensive than on Android. In fact, many apps that are free on Android, are paid apps on the Playbook. The main advantage of the Playbook is that it was 130 quid for 64 GB, and, as long as you can live with limied apps, it's a very nice O/S, and very nice hardware. But I wouldn't buy another!