Well I have used Fix-A-Leak before and it did the job. Mine was just a minor leak so I'm not sure how big of a leak your talking about but fix-a-leak says it can do some pretty big jobs so who knows. I have not used any other type of leak stopping liquid so I cannot speak for the rest of them. Fix-a-Leak isn't very expensive and it's not going to hurt anything so why not give it a try? Here is a link to the company I purchase all my supplies from including Fix-a-Leak and the price is very affordable.
The Hot Tub Lady.com - Fix-A-Leak.
Good luck!