Hey Swechha, Go ahead with dayara bugyal .. As they say dayara s the Queen of meadows and you get a lots of snow in December ... it's also a little challenging comparing to a easy trek like Nag tibba ... Dayara s also less crowded comparatively ... Happy Trekking !!!
Hi Swechha, both of these are different kind of treks. If you want to just enjoy snow with a small nearby trek you can go for Nag tibba, the views are not going to be really spectacular. But if you want to enjoy 360 degree of snowclad mountain peaks, endless snow covered meadows, go for Dayara Bugyal. Of the two you have mentioned Dayara Bugyal is the better choice.