Bali in January

Hi folks. i'm travelling to South East Asiafrom late Dic to early Feb. I'm starting in Kuala Lumpur, and planning to cover peninsular Malaysia and Thailand. I was also planning to go to Bali for a few days, so my question is: how's weather in Bali in Jan? Is it busy? Is it worth visiting in that month? Thanks in advance!
Oh, besides, any suggestions about peninsular malaysia's east coast around tha period? Is it that rainy that's not worht visiting if interested in beach life?

Martin, Argentina