You are the lead network engineer responsible for designing a complex global network infrastructure for a multinational corporation. The company operates in diverse geographical locations and requires seamless communication between its branches. You must choose a routing protocol that balances efficient routing updates and scalability. Which routing protocol should you select?

Given the requirements of designing a complex global network infrastructure for a multinational corporation with diverse geographical locations, the routing protocol that would balance efficient routing updates and scalability is the Border Gateway Protocol (BGP).

Here's why:

1. Scalability: BGP is designed to handle thousands of routes because it's used on the internet. This makes it suitable for a multinational corporation with diverse geographical locations.

2. Efficient Routing Updates: BGP uses incremental updates, which means it only sends updates when there's a change in the network. This reduces the bandwidth used for routing updates.

3. Policy-Based Control: BGP provides a high level of control over the routing updates that are sent, received, and installed in the routing table. This is crucial for a complex global network infrastructure.

4. Stability: BGP is a very stable protocol because it uses various mechanisms like hold-down timers, keepalive messages, and route dampening.

5. Interoperability: BGP can work with different Interior Gateway Protocols (IGPs) like OSPF or EIGRP, which might be used in different branches of the multinational corporation.

Therefore, considering the need for efficient routing updates and scalability, BGP would be the best choice.