For inter cropping I would recommend the Moringa, the nutrient dense leaves can be made into an excellent, folliar fertilizer, or used for mulching, the leaves have high levels of growth hormones, and studies with some other Mango related crops ( cashews ) has shown they help with some fungal problems.
Neem also has many good traits but the foliage is much more dense, and would block way too much light, they seem to grow wider.
Both these trees are amazing though, and I would include them on any permaculture project. Neem is a beautiful tree, and I have seen it grow in very arid regions on the Island here in the DR. only care is to get it established and protect from goats, both trees are multipurpose, coppice very well, drought tolerant, and can benefit other crops in one way or the other, but Moringa does better growing along other plants, you could plant strategically where it would partially shade a tree you want to protect during harsh summer, and cut it back in winter.