We have found that the FICO score is the most popular with lenders (mortgages, cars, etc.) so we order this one in order to check their score. You can order just the report or add an ongoing service from myFICO.com. Many credit card companies and banks now offer a free credit score on a weekly or monthly basis. We have had mixed experiences with these services. The score varies as much as fifty points. When you read the disclaimers, it’s often an approximation of the score.
Yes, Credit Karma is free but again not always very close to what a potential lender will see for their score. If “close” is good enough for your efforts, then it might work, but that is for you and your client to decide.