Slang for "Good":
General:
* Awesome: (very good)
* Brilliant: (very good, impressive)
* Cool: (good, enjoyable, stylish)
* Epic: (very impressive, memorable)
* Fantastic: (excellent, wonderful)
* Great: (very good, excellent)
* Rad: (cool, excellent)
* Sweet: (good, enjoyable, nice)
* Wicked: (very good, excellent)
* Amazing: (extraordinary, incredible)
More Casual:
* Dope: (very good, cool)
* Fly: (stylish, cool)
* Lit: (exciting, energetic, enjoyable)
* Sick: (cool, excellent)
* Tight: (good, excellent)
* Boss: (excellent, impressive)
* Top-notch: (of the highest quality)
Specific Situations:
* Tasty: (for food, drink)
* Bangin': (for music)
* Killer: (for something impressive)
* First-rate: (for quality)
Regional:
* Ace: (British)
* Deadly: (Irish/Australian)
* Brill: (British)
* Cracking: (British)
* Top: (British)
The best word for you will depend on the context and your audience. Consider the formality of the situation and your relationship with the person you're talking to.