Equifax, Experian and TransUnion are the three major credit bureaus in the USA.
It's always a good idea to check all your credit reports from all three of those credit bureaus since each one of those three major credit bureaus contain different reports and information about your credit report.
CreditKarma.com is a good free credit score checking website which shows you information from at least two major credit bureaus but you need to contact the other credit bureaus to get your credit report from them.