BIT (Fenwick tree) handles point updates and prefix queries in with half the memory and simpler code than segment trees. Use BIT when you only need prefix sums or prefix XOR.
Use segment trees when you need arbitrary range queries (range minimum, range GCD). For subtree sums, either works. For subtree minimums, you need segment trees. BIT is also faster in practice due to cache efficiency. If you can solve the problem with BIT, prefer it over a segment tree.