That is a tough one for me to answer. I'm really biased, and can't stand most fading techniques. They are all pretty inefficient. Its because of the way CDs store sound, without a separate vocal channel. In other words, the vocal cannot be removed without loss of other sounds. It can never be 100 percent faded.
I think if you have the resourses, try fading it yourself first. There are many software programs that you can download and try for free if you are serious about making a good track. Try to fade the vocal just enough that you can sing over it without yelling, and without distorting the other sounds in the file. Its a very tricky balance.
If you are old enough, you could ask the dj at a karaoke bar to fade it for you, or play your faded track over the system. They are usually pretty good about this. At least you can get a good feel for how it will sound so you're not thrown off at the contest.
*** There will soon be a forum thread where you can ask the experts in the field of karaoke. They are much more experienced then I, and can explain all the details with a little more authority. They will also be running our contest this year. Details soon to follow.***