Both are pretty good...I'm in a school orchestra, and play a couple of instruments, and they can sound good.
I would say one thing though - you'll sound horrendous initially on violin, and people will hate you, whereas flute won't sound as bad - they're both slightly awkward instruments in their own ways. As a woodwind player, I'd overall recommend Flute, as it's closer to what I do xD But I play Guitar too, so I'm a Strings-ist too.
I guess I'm just being irritating here, so if you want my vote, try both for about six months. Practise a lot (equally between them though), and if one isn't working out for you, drop it. I did that, and I haven't regretted quitting Trumpet.