Hi Anil ! While looking out for a keyboard you should check out the following points :
1) The Sound - Most important factor imho. The tone, polyphony and all
2) The Keys - How do the keys feel, and how do they react to touch
3) The Features - Extra Tones,MIDI,I/O Ports etc are some very useful features which might be a deal breaker in certain cases
All in all, go try both of the keyboards,compare there features and understand what works best for you. There is NO better judge than yourself so you better take a good feel of them before deciding.
PS - In India, Casio keyboards are usually better priced for the same features as comparrd to Yamaha , so if you're on a budget I think you should consider the Casio CTK. They are a good entry level series.
But, that is secondary as i mentioned. The most important thing to look out for is - Sound. If it sounds good to your ears, go buy it !