Which pawn is better? whites d-pawn or blacks c-pawn? in the opening?

That depends on the position.

Generally speaking, pawns closer to the center of the board are considered more valuable than those on the wings. But as with everything, it depends heavily on the position.

 

--Fromper 

In the opening it's important to develop fast. Taking a pawn can cause another piece to come out to a more valuable position. The d&c pawns themselves don't really matter even though I personally like to preserve them on the center.

Mostly it is better not to take the pawn but wait for the opponent so you can make the move with your(knight/bisshop/other pawn) using the queen to take the pawn  is not recommendable. It leaves it vurnerable giving your opponent an advantage on developing by constantly attacking.

that's really hard to say because things can get wild in the opening, you could exchange your pawns and get different pawns in the different places.

     I have this dislike of giving up my d-pawn for black's c-pawn in normal Sicilian; though I know it's regularly done. Is there a better way to think about it and deal with it.?

Against the Sicilian I like the queen's fiancetto variation (1 e4 c5 2 Nf3 Nc6 3 b3... 4 Bb2... 5 d4) which leads to a more or less closed position with lots of tension on the central pawns.

 thx ivandth will try it- started looking at g3 closed Sicilian-what do yo fine players think?

Queen's fianchetto looks strong to me. Good control of the center squares. I usually play sicilian, except when the opponent does it. I've never used the g3 though, mostly d3. I think you can only know by trying them