Please help me understand this.

When considering the following three lines of scripture:

Luke 5:37 And no man putteth new wine into old bottles; else the new wine will burst the bottles, and be spilled, and the bottles shall perish.

  38 But new wine must be put into new bottles; and both are preserved.

  39 No man also having drunk old wine straightway desireth new: for he saith, The old is better.

For years, I always thought that lines 37 and 39 were likening the new wine to the new man, the new nature.

But if so, why would line 39 say that the old is better?

What, then, is the new wine, and what is the better old wine?