Confused between Canon 1200d and Nikon 5100D. Which one should i buy ?

SOURCE: i'm planning to buy a DSLR but confused what to buy

You have named several excellent digital SLR cameras aimed at the top end of the amateur/semi professional market.
I have the Nikon D200 and have been very pleased with it.
As stated by JCDill, you must really decide what you want and can afford. The camera body you choose will commit you down one path or another. For example, if you choose Canon, only Canon or OEM (Other Equipment Manufacturers) such as Sigma lenses will fit your camera body. Canon have a good reputation for their auto-focus, while Nikon make lenses that are the envy of others.
If this is your first digital SLR then you might be best buying an entry level body with a multi-purpose zoom lens such as the Nikon D40. There is a lot to learn.
If you are converting from film SLR and already have a set of lenses, then the cameras you mentioned will probably be able to use your existing lenses (but this is less so with Canon than Nikon). I was ecstatic to disover that my old Nikon 500mm mirror lens works in manual mode (with metering displayed) on my Nikon D200 but would not work properly on my Nikon D70.
I hope this helps.