What's better? Concordia University or Carleton University?

You will need to consider so much before making this choice as you have not specified any program so only a general comparison can be done on the basis of your budget and requirements. Major difference between Concordia and Carleton Universities is in their location, culture and opportunities. Your opted major and choice of city/environment will affect this choice. 

Pros and Cons for Carleton University:

• Well connected through buses, trams and cars. 
• Huge population with a variety of active nightlife and cultural life 
• Options of programs are limited, 50 academic disciplines. 
• Carleton University Campus is surrounded by many tech-companies, hence good chances of jobs.
• Recognized for its graduate employability by QS rankings.
• Renowned for its engineering programs with a dedicated center of advanced studies in Engineering.
• Accommodation costs and tuition costs are also cheaper at Carleton University.

Pros and Cons for Concordia University:

• Located in Montreal, one of the best student cities in the world
• Over 400 programs to choose from
• Acceptance rate and scores required are lower than Carleton University, meaning relatively easier admissions at Concordia.
• The faculty of arts of Concordia University is largest in Canada.
• It is French dominated which could be a problem