Hi,
I have implemented both of them but the expected wait time seems to be a better idea. The position in queue may cause misunderstandings when a call with a higher priority takes precedence (imagine: "You are the secon - oh wait, no, you're the third customer... er... wait, now you're just the fif... what am I talking about you're the fourth" etc)
The expected wait time is more meaningful. The customer actually knows he's going to wait and based on this information he may decide whether to start brushing his teeth or start a new episode of .
G.