Darren seems like a really Australian name for me. I don't think I've ever met one who wasn't Aussie. I quite like it, it makes me think of a young blonde guy, maybe a surfer-type.
Darrell depends on whether it's on a girl or a boy. On a girl it makes me think of an Enid Blyton character, I think from Mallory Towers. Very English and traditional, oddly. On a guy, it makes me think of a 40-50ish bloke, probably a tradesman, not particularly tall. Although I would spell it Darryl or Daryl for a male, Darrell seems a bit feminine (prob because of Enid Blyton).