If Angstron lets me use Firefox, office, and chat apps, and preferably switch between them, then I'll be using that, simply because it's simple, and it'll probably fit the screen-size better.
But I'll probably throw Ubuntu onto a card just to see it run.
That said I installed Ubuntu onto a 2.4GHz celeron laptop last weekend, and it ran worse than XP, with programs hanging approximately every minute or so, simply because the latop was a 256MB Ram model. So I don't hold out much hope for superb Ubuntu performance on Pandora with less processing power and equal ram.