Compare DSLR: Sony a37 OR Nikon 3100?

Which DSLR camera is better. Provide reasoning as well please.

They are both fine cameras.

The Nikon system has over 75 current lenses available and many more accessories than the Sony system.

Actually the Nikon camera that is as new as the A37 would be the Nikon D3200 and it has one of the best performing sensors of ANY entry level camera.

My guess is you are going for price over quality and/or performance

The Sony's an SLT, not a true SLR, making it better for video.

Beyond that, only you can answer the question. Find a dealer who'll let you handle them and see how they feel.

Sony make some very nice cameras, and users love them, generally buying them because they want them, rather than listening to the Canon/Nikon fanboys (many pros rely on the big two because they've always done - that doesn't mean they're the best).