Which one has a more extreme topspin backhand grip? Who puts more spin on their backhand, and who drives it flatter?
Whose backhand would you take against Nadal's forehand?
Almagro looks to have the more extreme grip (extreme eastern). Wawrinka hits with a more standard eastern grip.
Compared to Wawrinka, who has a more linear swingpath, Almagro generally hits with more topspin - you can see he moves the racquet head up and across the ball as he hits it, which is quite unusual. He also meets the ball further in front of his body, and probably has the best single-handed backhand for dealing with high balls on tour.
Having said that, as pointed out Wawrinka's BH is better off clay, and he probably has the better slice backhand. I also prefer Wawrinka's BH DTL, and his backhand in general has more power and weight of shot behind it.