Re: I'm touched by the weirdness of this request...
I really would start with the first two with the proviso that if you don't enjoy them all that much you don't stop at that point.
I don't like that suggestion. I don't think it's fair to make people do the less fun stuff first, in order to pay for the good later. And I think you also need to have read a bit of fantasy first, to see what 'the Colour of Magic' is laughing at.
Much better to read the other stuff first, then come back if you're enjoying it. Whereas I think the first few books can be a bit off-putting. Lots of people have said to start with Mort, but I personally feel that's one of his weaker ones - while he was still learning to be an author, and developing a style.
I've never even been motivated to go back and re-read 'Stata' and 'Dark Side of the Sun', and I suspect if those had been the first of his books I'd tried, I'd never have read any more. Colour of Magic is good, but less good and of a much narrower appeal.