Formal:
* Prazer em conhecê-lo(a). (This is the most common and polite way to say it)
Informal:
* Prazer em te conhecer. (This is more casual and can be used with friends or family)
* É um prazer te conhecer. (This is slightly more formal than "Prazer em te conhecer" but still informal)
More casual:
* Legal te conhecer! (This is very informal and can be used with close friends)
It's important to choose the right phrase depending on the situation.
For example, if you're meeting a new client or colleague, you would use "Prazer em conhecê-lo(a)." If you're meeting a friend of a friend, you might use "Prazer em te conhecer."