Final answer:
An SSH client is the preferred tool for securely accessing a Base tier firewall via SSH, offering a secure method of connection over unsecured networks.
Step-by-step explanation:
To access a device such as a Base tier firewall via SSH (Secure Shell), the preferred tool is an SSH client. SSH is a protocol that provides a secure channel over an unsecured network in a client-server architecture, offering more security than Telnet, which sends information in plaintext. While Putty is a popular SSH client for Windows, the term 'SSH client' refers broadly to any client software that facilitates SSH connections and could include tools like OpenSSH on various operating systems including Linux and macOS. Therefore, in a general sense, option 2 (SSH client) is the preferred choice. Telnet and FTP clients are not suitable for SSH connections as they serve different protocols and use cases, with Telnet being less secure due to its lack of encryption, and FTP client being used for file transfers.