When comparing swig vs EJS, the Slant community recommends EJS for most people. In the question“What are the best JavaScript templating engines?” EJS is ranked 6th while swig is ranked 14th. The most important reason people chose EJS is:
EJS uses all the JS jargon and logic, so if you're proficient in JS, you can use EJS right away.
Ranked in these QuestionsQuestion Ranking
Pros
Pro Works both on the client and on the server
Available for node.js and major web browsers
Pro Does not hide HTML
Swig does not abstract HTML syntax from you (like e.g. Jade does) giving a certain filling of control over the markup.
Pro Complete JavaScript logic
EJS uses all the JS jargon and logic, so if you're proficient in JS, you can use EJS right away.
Pro Same language before and after rendering
Your html/text remains pretty much the same before and after rendering. EJS filters out and performs its functions on any occurrences of its own <%= %>
tags in your template.
Pro Lightning-fast to learn
EJS introduces fairly small amount of new syntax that one has to learn to become fully proficient. The syntax itself is easy to comprehend for anyone who is even somewhat familiar with JavaScript and CSS.
Pro Consistently scores rather well in benchmarks
According to some benchmark tests, EJS is way faster than Jade or Haml.
Pro Powerful error handling
EJS has a really smart error handling mechanism built right into it. It points out to you, the line numbers on which an error has occurred, so that you don't end up looking through the whole template file wasting your time in searching for bugs.
Cons
Con No updates for at least 6 months
Swig has not received any new commits since June 25 2015.
Con No support for block by default
EJS has no support for the block
functionality which allows you to reuse pieces of templates across different files. Although it can be added to EJS through a third-party library.

Con Cryptic syntax
Much more difficult to read, especially for designer/HTML people who don't write JavaScript.
