Tell them its more reliable and OSX doesn't get viruses. But the best way to prove Macs are better than Windows PCs is to hope it works according to this plan.
1. You own a Mac because you had so many problems with your Windows PC. Correct?
2. Hope your Mac lasts longer than your PC. (Take VERY good care of it)
3. Show your parents how after a few ears, its been a great machine, and its still running as fast as it did.
1. I had never had a bad experience with a PC. I am typing on a 6+ years old Dell Dimension 4550. I never had any bad problems with it. My recent PC laptop was a HP DV6T Quad with i7 that I bought on Black Friday for $622 after 20% bing cash back and that $450 HP Coupon. I sold it for $700 after 7 months of use. I have never experienced any problems with a PC what so ever.
2. I hope they do last as long.
3. Well I don't think it will last a few years. What I like about Macbooks is that they retail their value. When they release a new Macbook style, this one will go up for sale.
As for the virus thing, I never get viruses on my PC. I go to trusted porn sites with no viruses in them.