my results, after 200 attacks or so on valleys lvl 1-4 over 4 days i got: 3 lion, 5 rose and 3 cross.

how i got them:
-use mayor with high intel (65-80+).
-for rose medals attack valleys lvl 1-4 (haven't got ANY from npc's)
-attack as many as possible at one time (i was hitting 8-11 at one time)
-make sure the valley has a full army, after attacking wait at least an hour after abandoning the valley before attacking the same valley again.
-i just used warriors since they're cheap and fast to make..
-make sure each battle is close and you're taking casualties (lvl 1 i'd send like 75 or so warriors)
-use a spreadsheet or piece of paper to keep track of which valleys you're attacking so you don't have to look for them on map screen which can get REALLY laggy

hope it helps..