I watched the Others when I was about 12 and scared me to death.It's just so tense. Watched the Ring last week and it scared the **** outta me.The Descent made me laugh but it was quite gory and I did have to close my eyes at some point due to too much blood.
You can't really compare them since they are very different films but I'd probably rate them as:
1.The Ring
2.The Others
3.The Descent
I'm sure the Others would still terrify me if I watched it now:P