From maintenance point of view – Huawei is the best.
It has embedded traces for all interfaces and protocols(ISUP, MAP, SCCP, TCAP; CCS7 links,R2, A,C,D interfaces). You can very clear see all meassages in readable format (no HEX or BIN). All messages are decoded – so no need special knowledge to understand it. Even high level managers can understand it 🙂