Thailand.
1. The weather is perfect for dec-feb.
2. You're on a honeymoon, you'd definitely enjoy this place for multiple reasons.
3. Bali is too crowded because of the fame it got lately.
Hey Sanju, I would say that both Bali & Thailand would be good, but it all depends on what you're looking for (experiences) and what's your budget! Bali would be slightly more expensive than Thailand :)