Store credit card effect on credit

Hiya,

I'm currently looking to buy a laptop from best buy, however I want to be able to finance it over 12 months so I am thinking about applying for their store credit card. Does anyone have any experience with it? Do store credit cards hurt my credit score more than a normal credit card?

Additionally, my Discover account says my FICO score is 756 but on Creditkarma my two scores are 689 (Transunion) and 684 (Experian). Why is there such a discrepancy?

Thanks!