Most common:
* 高兴 (gāoxìng): This is the most general and common way to say "happy" in Mandarin. It expresses a feeling of joy or contentment.
Other options:
* 快乐 (kuàilè): This means "happy" or "joyful," and is often used to describe a feeling of being carefree and lighthearted.
* 幸福 (xìngfú): This translates to "happy" or "blessed," and is often used to describe a state of deep contentment and satisfaction.
* 开心 (kāixīn): This means "happy" or "cheerful," and is often used to describe a feeling of lightheartedness and enjoyment.
Which one to use:
* 高兴 (gāoxìng) is the safest choice in most situations.
* 快乐 (kuàilè) is good for expressing a more carefree or joyful feeling.
* 幸福 (xìngfú) is more appropriate for describing a feeling of deep happiness or contentment.
* 开心 (kāixīn) is good for expressing a feeling of being cheerful and lighthearted.
Examples:
* 我很高兴见到你。 (Wǒ hěn gāoxìng jiàn dào nǐ.) - I am happy to see you.
* 我今天很开心。 (Wǒ jīntiān hěn kāixīn.) - I am happy today.
* 我希望你幸福。 (Wǒ xīwàng nǐ xìngfú.) - I hope you are happy.
* 祝你快乐！ (Zhù nǐ kuàilè!) - Happy (for you)!
The best way to choose which word to use is to consider the specific situation and the nuance you want to convey.