There are players of this game who have dedicated lots of time and effort to helping us fellow players. But the developers of this game have changed how medal collecting works post beta (DUH). However Rose medals will be best found in Swamps lvl 1. Today alone I "farmed" 50 attacks (and here is the key for effectiveness) You need 1500 scouts (decreases time for attacks as you know) Spend your resources on building scouts so you can make these attacks.
For those of you trying to reach the elusive Title of Baronet, fret not because it will help you in your quest. You will get more lion and cross medals but so far I'd hit a rose medal 1 in 7-10 times when I attacked a level 1 swamp. I gained 7 Lion Medals 5 cross Medals and 5 Rose Medals.
It may be more difficult, but using scouts in 1500 or more on lvl 1's will help you get what you want for FREE.