Advantage of slate roof versus shingle roof?

I am looking to buy a house which has a slate roof in need of repair (lots of leaks). Some friend told me that I can get some company take the slate and change to a shingle roof for very little money compared to have the slate roof repaired. Are there advantages to one or the other kind of roof? If there are no particular advantage to a slate roof I might as well change to shingle if it would save me a lot of money.