There are over 50 different flavors of FICO scores (which are not what you see on any of the free sites - Credit Karma, Credit Sesame, Quizzle, etc.). FICO scores are what over 90% of creditors use when determining someone's credit worthiness.
There are Auto Enhanced FICOs, Bankcard, Mortgage, etc. You name it, there's probably a FICO for it. Depending on which version the creditor is using, your scores can fluctuate dramatically. A 750 on a FICO Score 8 could be a 675 on a FICO Score 5, which could be a 700 on a FICO Bankcard Score 4.
I use credit cards in the manner that I would use debit cards to get the reward points/cash back. I pay off almost everything immediately after the charges hit, and have no more than 10% utilization reporting every month.
I heard FICO is the only important score, but it seems like Chase used a TransUnion based score (with a range of 250 - 900 apparently..weird) to determine my credit worthiness.
Do you pay for your score or anything? I may request a free credit report but I don't have any intention or pulling out a huge loan or a house right now but it's nice to know.