My friend has the D3100 and he is very happy with it. He makes awesome pics.
I've got a D3100, and it really is the best camera for the price. The D5100 is better, but I doubt you'd notice much of a difference below ISO 1600, and it's not really worth the extra cost unless you really need such high sensitivity, IMO.
All in favor of 3100
I see. Thanks for your input, everyone.
Nikon D3100 body is 241EUR
Nikon D5100 body is 330 EUR
D5100 has better resolution, swivel LCD - which is good for making strange angle shots and video. It can film with a little bit higher fps. It has microphone jack. It supposedly has better HIGH ISO performance (although I rarely use ISO higher than 400). It has a newer sensor, but it's impossible to find side by side comparison photos on the net.
D3100 is almost 100EUR cheaper, which can buy me some extra lens or flash.
Anyone of you has D3100 and can swear by it? Or maybe 5100?
It's intended for my gf's birthday, and I don't want to spoil a surprise by asking her opinion. Canon and other brand's are out of the question, as we have some nikon lenses with our old d40 already.
Get a smartphone that have really good mega pixel instead?
No, just no. That's two different worlds.