I (note the capitalization) wouldn't say that either is really more conducive to building comaradery (note the second 'a'). Spending weeks together in a 10-man tent can really pull you together, but it can also make you want to drive your bayonets into each other. On a summer Ex, you actively seek your buddies, and on a winter Ex, you spend more time with your section, 'cause it's too cold to go looking for anybody. But, even then, you try to find time to go poke your nose into a friend's tent. Or, in both, you tend to gaggle together whenever the opportunity arises.
If it's a really good Ex, you're too busy to to do much but patrol, stand watch, and sleep. You want to build comaradery, be a good comrade. It'll be returned.
Worry about building morale later, anyway. Focus on the 100 meter target. You can start aiming at the 500 later.