Formal:
* 今晚 (jīn wǎn) - This is the most common and neutral way to say "tonight." It is suitable for most situations.
Informal:
* 今晚上 (jīn wǎn shàng) - This is a more informal version of "今晚."
* 晚上 (wǎn shàng) - This literally means "evening" but can also be used to refer to "tonight."
Other options:
* 今天晚上 (jīntiān wǎn shàng) - This literally means "this evening" and is a more specific way to say "tonight."
* 这晚上 (zhè wǎn shàng) - This is similar to "今天晚上" but is less common.
The best way to choose the right word is to consider the context of your conversation. If you are unsure, "今晚" is a safe choice for most situations.