대박! (daebak!) as an exclamation means "Awesome!", "Very Cool!", "Wow!", "I can't believe it!", or something in that sense.
You can use it as: 대박이다!! (Awesome!!)
짱! (jjang) as an exclamation means "Good!", "Top!", "The best!", or something like that. It also has similar meaning in a sentence and sometimes it can mean "really" or "very".
이것 짱이에요 means
"this thing is top-class", "this thing is the best", or "this thing is super."
니가 짱이야 means "you are the best!" or "you are awesome"
I think this two words is similar, but I think 대박 is emphasizing that something is awesome, and 짱 is emphasizing that something is the best.