Nikon J1 or Nikon D3100 for beginners?

Which one, and why.

Definitely the D3100 as it is cheaper. Its a real SLR and not an EVIL. It has APS-C sensor. Lower noise. You have MANY lenses from different brands and MANY flashes from different brands to work with. But if you are looking for great quality in a tiny package small enough to be tucked in the pocket and taken to parties and such, then any EVIL (Electronic Viewfinder - Interchangeable Lens) should do the trick. But if you are serious about photography, SLRs are much better in each and every way. Cheers for your upcoming camera!

The jury is still out I think on the J1, but I'd spend the money on a D3100, especially if you see yourself buying new lenses over time. You can wrap up a lot of money in a MILC - Nikon or any other brand - and end up paying as much for it as a bona-fide DSLR,

I have never seen the advantage of MILCs due to the cost factor.

The only real advantage I see is for travel or vacation when you want to travel light. But for that, you pay a hefty premium in terms of the cost.