Personally, in a case like this, I would pick the one with the larger Field Of Vision. Typically, the larger the objective, the larger the FOV, however, the higher the mag, the lower the FOV. These two scopes might be close enough in dimensions that the two overlap, maybe the 3.5-10x has a larger FOV even though it's higher mag. because of it's larger objective.

Either of these scopes are going to be low profile enough to use on low rings/mounts, and they'll be pretty similar in weight (a fixed 4x would be lighter still), and I'm guessing the other exterior dimensions are pretty similar, so personally, I'd call them equals and base my decision on the FOV. If the 3.5-10x has a bigger FOV at it's lowest mag, then get it, the extra magnification will help your accuracy, and the bigger objective increases your light capture, and if it has a larger FOV at 3.5x, it's better for hunting at close ranges than the 2.5x.