To me, Dumbledore is a very trusting person. Obviously we see that with Snape, and the line 'I would trust Hagrid with my life' in SS/PS shows how Dumbledore is extremely trusting. And we saw how Snape came out; Snape killed him.
That said, I think it would be difficult to decide which method he would use. If it were someone that he knew well, yet did not trust, I feel that he may remove a section of their memory. Somehow, I could see him obliviating McGonagall more so than, say, Malfoy, because I can't see him "getting revenge" on someone - even his worst enemies.
However, people he was friendly with but not close, I would imagine he may. But he would do it kindly, telling them, "You needn't know this. I'm taking it out of your memory. Is there anything you'd like to put in the Penseive?" instead of just plain "Obliviate!" out of nowhere.
Snape, I cannot see Dumbledore doing that to. I think he would trust Snape with something big, and trust that he would not tell. However, if it were something regarding Horcruxes, in one sense, I think he may remove it from Snape's memory. In another, I can see Dumbledore telling Snape. It just strikes me that Dumbledore may trust Snape with something like that.
Looking back, that's a pretty long post. :o
But I'll finish with this:
Dumbledore was a mysterious man.
Hope that's what you were talking about.