I successfully sued the church for return of a considerable sum of "donations".
In my opinion it all depends on what you are suing them for, which country you are taking your case to, and how much evidence you are able to get against them.
In my case they spent a considerable amount of time, and their money ultimately, in trying to get my case struck off, rather than fight the case.
In the end they gave in because they didn't want their dirty laundry aired in a high court populated by media reporters.
Speaking for my case I would say that it was like one big game of poker. Who has the biggest financial availability? Who can produce the biggest amount of dirt against the other participant? Who has the most to lose, or gain?
I had nothing to lose and everything to gain, and I was fortunate enough to have financial backing.