I use both Credit Karma and myFico. All things considered, I prefer CK.
Your "real" score, most likely meaning your FICO 8 score is the one most lenders will pull. Credit Karma uses the VantageScore models. These are models created by the 3 bureaus to compete with FICO. That can either be 20 or so points lower or higher than your FICO score. My FICO has always sat 20 points higher.
The reason I prefer Credit Karma is that it gives me a weekly update to what's going on with my credit situation in, honestly, a friendlier way. And their simulator is based on your latest score unlike myFICO which only factors in your quarterly scores for their simulator which makes real world short-term predictions rather useless.
The value that comes from myFICO is the fact that with the 3B package you'll get automatic updates as soon as something is reported to the bureaus. That and getting your actual FICO scores is a benefit. Outside of those two things, for $30 a month, it's not particularly worth it. I'm about to drop it as I just wanted to test it out. Only had it for a couple of months and I think I'd be ok with just having CK.
I'd say it's useful if you want those very narrow benefits and have $30 in disposable cash every month. If you don't want to spend any money to know what you basically already know then I'd say go for Credit Karma.
Using CK to track my credit card usage over the short amount of time I've even had a history I've managed to meek out a decent credit-lending score. And I've also managed to help a couple family members using it. Invaluable tool for the price, imo.
