Nikon D90 is best or nikon d3100 is best?

Please tell me which one is best and why /?

D90 is better and advanced than D3100…
If you are a beginner, them d3100 is the best suited for you. If you have been doing photography for quite some time or are familiar with all techniques then D90 is for you…
Chose what you need at the moment.

D90, the ergonomics are far superior with dedicated buttons and a penta-prism viewfinder. It also has an auto-focus motor so you will not be limited to AF-S lenses like you would on the D3100.

The D3100 is adequate for the beginner, but you will quickly grow out of it.

D90 is much better. But by asking the question you show that you haven't done any research so the D3100 is probably better for you.

The D90 is a much more advanced camera. Its replacement is the D7000.

The D3100, while a fine entry level camera, does not live up to the standards of the D90 or D7000

What's a bit confusing for me however is the fact that the D3100 has better mega pixels over the D90 (12M vs 14M respectively) and also has a better ISO compared to the D90 as well, and at the same time it's much cheaper! Both cameras have a video but it seems that the D3100 produces a better quality HD video. However the "video thing" is not an issue to me as I'm after photographic specs rather than video specs. But as said before, the D90 is 50% more expensive with 2 years older technology than the D3100!

The Nikon D3100 is an excellent entry-level camera. The disadvantages (for some people) are the lack of bracketing, small size and slow burst speed. If you are serious about photography, I suggest spending a bit more and choose between the D90