Jungle
There are no two ways about it: the jungle is basically hot and steamy. Having said that, it is certainly less steamy in the dry season (April-October). In many ways, however, travel in the wet season is better, as higher water levels mean that more of the jungle is accesible by small boats, and this is usually the easiest way to get around. For a good combination, try travelling in April or May, when water levels are still good, but the rain has eased off!