Credit scores are determined by a number of factors including:
Number of accounts open, number of delinquent accounts, age of accounts, available credit on your accounts, number of inquiries
And so on...but that is a general list of items they look at. Obviously the more accounts that are paid on time over a long period of time is better.
The reason different credit bureaus have different scores is because not all creditors report to all 3 credit bureaus. Some creditors might just report to 1, others might report to 2 or 3. So some credit bureaus might have all your credit accounts and another credit bureau might only have your negative credit accounts.
Generally you want to credit score at 700 or above, so not to have any problems. Anything below that and you can be denied credit based on your score. A good way to boost your credit score is to do some credit restoration . Removing the negative items off your credit will help.
Good luck and hope this info helped.