If you are a half orc you can get 18 str/18 dex, which I think would be the best case. Comparing to scale armor with MW bonuses and stat increases:
lvl 1: hide ac 17/scale ac 17
+2 armor (say lvl 6): hide ac 21/scale ac 22
lvl 8, still +2 armor: hide ac 24/scale ac 24
+3 armor (lvl 11): hide ac 26/scale 27
lvl 14 (+3 armor): hide ac 29/scale 29
+4 armor (lvl 16): hide ac 32/scale 32
+5 armor (lvl 20): hide ac 35/scale 36
lvl 21 (+5 armor): hide ac 36/scale 36
+6 armor (lvl 26): hide ac 40/scale 42
lvl 28 (+6 armor): hide ac 43/scale 44
If you are using the masterwork armor rules from phb2, scale gets an advantage every time you get an extra + on your armor, which cancels out with the stat bonus you gain every second stat boost lvl (8, 14, 21, 26). What is best depends on if you get +2 armor before or after lvl 8, and so on. Scale pulls ahead in late epic with Elderscale's +13 (and extra point), but hide armor gives +1 or +2 to fortitude defense at +1, +2, +4 and +5 levels.
Plate armor gives a better bonus than both, but requires a feat (and high con). Also note that scale specialization only requires 15 dex while hide specialization requires con 15, something you can't get until lvl 21 if you want dex/str 18 and are pumping both every level to keep up your ac in light armor (max 13 con at lvl 1 with normal point buy). If you plan to take an armor spec feat at paragon, Scale is the better option (and gives you extra speed to boot).
But having said all that, the difference is pretty minor, 1 point of AC at paragon and when you get a new level of magic armor before stat increases, 2 points at late epic with spec feat. Extra fortitude defense from masterwork hide armor isn't bad. But you have to pump dex every chance you get.