Like it has been said in the thread already, most of the maps in DoD:S were designed to be favored for the Axis(Wehrmacht). Some of you might wonder why that is. Perhaps the fact that the game is set to be played in WWII might give an indication. Most of the battles for the Allies were not in their favor, especially initial ones in 1944 with the Invasion of Normandy. In general, Allies had to fight past fortified positions that were more advantageous to the Axis. Keeping in spirit of that, most maps in DoD:S are better for the Axis.
With that said, it really isn't fair to say that maps are unbalanced in my opinion. It takes more than the shape of the map to determine who wins and who loses. You just need to have teammates that work together to win the match. In addition, team coordination with spotting sniper and machine gun positions along with noting the positions of other enemies can really turn the tide of battle. Next, encouraging your teammates to move up or telling them good job on the kills can really bring a team together. Finally, playing a map to the point where you know how long it takes to get certain places or knowing all the spots people go can really help a team out.
So, if you really want an answer from me, I would have to say that:
Donner, Kalt, and Flash often tend to be maps that are associated more with stalemates. To me, that indicates they are maps that tend to be more balanced. They are also similarly designed with both sides being relatively symmetrical. Also, the maps are mainly flat, which helps with balancing.
Anzio can be very similar in that regard, but I feel there are often too many ways to flank on that map for it to stalemate very long. I think that the Axis has a slight edge on getting the first point than the Allies do. It is harder to defend the well as Allies compared to the fountain of the Axis mainly because of the window and the fact of less space to exit the spawn exists there for the Allies.
Strand is designed to be unfair, so I suppose it may be fair to say it is the most unbalanced. It really isn't the best representation of the landing at Omaha Beach, but that is its intent. By far, the map requires the most coordination and teamwork on the side of the Allies along with spotting snipers and mgs.
Avalanche I feel is actually one of the best maps. It has always been my favorite because of the opportunity to completely disorient a team and take down 10 people in no time at all. Maybe my intense familiarity with it makes me think it is not really so unbalanced. Sure, the map is designed to be advantageous for the Axis, but it is just as easy for both sides to shut down the enemy team. I feel it tends to be somewhat easier for Axis to win on a more consistent basis, but I have gone round after round winning with Allies. This map probably comes in second in terms of teamwork and coordination required to win.
Argentan is probably one of the best maps in terms of balancing, but it really is not so fun when you're losing the game or down to only one point. It is nice that the mid point is on a hill and so both teams have the opportunity to gain the high-ground advantage. Axis I think tends to be able to get to mid slightly faster that Allies, though. In my experience, usually the map tend to be lopsided for awhile then switches. Good teamwork and coordination does tend to come into play here.
The most balanced maps most likely are orange maps because they are often the most symmetrical. However, you do tend to run into more hackers on these maps since they are often most associated with a death match type game play or gun game.