Well you kick the crap out of people who have both troops and spies... Unless their stats are larger than yours >.>
Attack is your classic bully who beats people up. Spies is that quiet kid in the back of the class that never says anything and is bullied, but one day he has an insane comeback and the whole class riots.
Time for a real answer! Spies are great- they allow you to sneakily take gold out of your opponents coffers without ever being detected. Also important for strips! However, the gold you plunder is directly related to how many spies you have. Meaning skin stealing is most profitable. This is made up for by having more options, spies also scout and assassinate to make up for their lack of gold plundering efficiency. Attack build is like walking up to enemy kingdom and tearing their doors down and holding the king at sword point until your army and allies grab all the gold they can carry home with you. The plunder is better because it accounts ally bonus, which steals don't. Meaning you'll always have a baseline of gold, no matter where your troop level is. Of course skimming is still most efficient, but you'll never have last hit getting 24,000 gold. Woopdeedoo. In summary. Attack- more gold Spies- more options of attack
Depends on your play style really On an old account I used to osf for pwars so I've had a spy-esque build ever since (despite quitting and returning every few years)
In my opinion, attack builds don't really make more gold. I have both a hansel and a attack build, and I prefer my hansel when it comes to gold making. When they were the same size, my hansel was making around 160 mil a hit on hte while my attack build makes 150 and drops all the way to 120 mil last hit. Sure they can hit harder, but id personally go with spies.