When comparing PuTTY vs Extraterm, the Slant community recommends PuTTY for most people. In the question“What are the best terminal emulators for Windows?” PuTTY is ranked 8th while Extraterm is ranked 24th.
Ranked in these QuestionsQuestion Ranking
Pro De facto standard client for SSH, Telnet and Rlogin
PuTTY is one of the oldest and most popular clients. It has earned the trust of a great number of users over a long period by being reliable, offering useful features and helpful support. It got into the 15 Essential Open Source Tools for Windows Admins list by InfoWorld.
Pro Source code available
Full source available. Compile and modify it yourself.
Pro Can be used on any Windows computer, even without admin rights
Pro Lightweight and portable
Doesn't require much resources (memory and hard-disk). Can even be run on a system by just downloading without install.
Pro Supports tab, splits and panes
You can set up your own layout with multiple splits and tabs.
Pro Shell integration
The shell integration makes it possible to group in command output in "frames" which show success/failure.
Pro Image support
You can view images and other data types like audio directly in the terminal.
Pro Keyboard based text selection
It is possible to go into a cursor mode where you can select text just like in a text editor. It even supports multiple cursors.
Pro Global shortcuts
You can configure global shortcuts to open the terminal.
Pro Keyboard friendly "Command Palette"
Just like Sublime, Atom and VSCode you can easily search and find commands from the drop down Command Palette.
Pro Cross platform
Con Can not save passwords
Anyway, you can use "PuTTYgen" to generate a key pair, then use "Pageant" to do a password-less SSH remote login.
Con Ugly design, too simple
Looks very dated. Does the basic functions very well, but not much more.
Con Lacks features
It is JUST an SSH client. There are many other options with built in X-servers, Multitabbing, etc.
Con Tedious logging/tracing
Its tedious to set up logging and tracing (e.g. for serial connections).
Con No global settings
If you want to change a setting for all your connections, you'd have to do it individually.