Final answer:
The recommended license type to collaborate with potential customers on Chatter is Chatter External.
Step-by-step explanation:
The license type that I would recommend for the sales rep to collaborate with potential customers on Chatter is Chatter External. This license allows external users, such as potential customers, to access and collaborate on Chatter without requiring a full Salesforce license. With a Chatter External license, the sales rep can invite and engage with multiple potential customers on Chatter, keeping them informed and connected.