Copy/paste from Evo mailing list from Ben Roberts - http://mail.gnome.org/archives/evolution-list/2009-June/msg00124.html :
-------------------------------------------
This problem concerns the order of preference of emails when these are
added to a Contact. I might expect that the "first" email (as entered in
the Contacts dialog) is the "preferred" email (e.g., displayed on the
Contact's address card when this is formatted in the list, first choice
for sending emails to); and that as you go to the second, third and
fourth email fields the priority goes down accordingly. But it seems
that in my installation the reverse is the case: that an email entered
in the last field takes precedence over fields 3, 2 and 1, with 1
apparently receiving the lowest priority (empty fields excepted).
-------------------------------------------

... adding my own comments now:
-----------------------------------
I can confirm this, and the current used order seems to be this in the contact's details:
[ email 4 ]  [email 2]
[ email 3 ]  [email 1]

For English-speakers, I imagine the general expectation would probably be that the order should match the order of reading text (left to right, top to bottom), i.e. top-left should be email 1, top-right should be email 2, bottom-left should be email 3, bottom-right should be email 4, although the positions of 2 and 3 could maybe be swapped if people expected this ordering.

I.e. my guess is that most English-speakers' mental model is probably this, and that Evo should probably try to match it:
[ email 1 ]  [email 2]
[ email 3 ]  [email 4]
-----------------------------------

Other information: