Arosa is a decent car but the boot is pretty much pointless.
I had one as a loaner and couldn't even fit an archive box in the back without dropping the rear seats.
If you absolutely have to have one, make it the GTI (edit, think SEAT call it an Arosa Sport (1.4 16v) - VW equivalent is a Lupo GTI)
If you like the Ibiza/Fabia, don't rule out a Polo. 1.4 16v petrol is a nice engine on the revs.