I worry that believing that store cards are beneficial to the mix and FICO score can cause people to take actions that they may not need to. You may or may not want a store card – but the reasons for having one should be clear to the one who app's.
Although much of FICO scoring is under wraps, the FICO codes are published.
They want you to have an open revolving account with a bank or national credit card co. (That’s code #3 – you're dinged if you don’t).
They want you to have activity on that bank or national account (Code #15 – dinged if you don’t)
They want you to have a revolving account (That’s code 16 – dinged if you don’t).
By having a bank card, you hit two birds with one stone (#3 and #16). By using it, you meet the requirements of #15. After one bank card is in place, you don’t have to worry about whether a card is a store or bank card. FICO does not have a code for and does not ding you for not having a store (merchant) card.
That being said, there are some advantages to store cards. For rebuilders, they tend to be easier to be approved for, may have higher CL’s than rebuilder bank cards, and tend to be long-lived so they add to your AAofA over time. Some store cards offer customer perks. So bank cards and store cards both have a niche. Bank cards definitely help your FICO score in and of themselves. Store cards can help with higher rebuilding CL’s, long-term AAofA and cardholder perks. You can (and some may argue should) get to the 800’s without a single store card in sight. DH was at 802 with one ($500CL) bank card only.
I’m a rebuilder – so I’m quite fond of my store cards. But I did not receive a FICO score increase--in fact I gained many points with my first bank card, but lost points with my first store card. DH and other posters have had the same experience. Mine is a Macy’s and it serves my needs well – but not because of FICO scoring practices. I also have GEMB store cards – again because I’m a rebuilder and they meet my needs. I have one bank rebuilder card, an Orchard. I will not cancel my Orchard in spite of its AF, until I open another bank card – because bank cards do impact your FICO score.
The only place I’m seeing how the account is showing up for the CRB’s is on my CCT inquiry page. Is anyone finding a better place – maybe one that shows all active accounts? For what it’s worth, these are the codes that show up on our reports:
Cabela’s: National Credit Card Co.
Cap One: Bank Credit Card
FIA CSN (Bank of America): National Credit Card Co.
GEMB (Care Credit Card): Sales Financing
GEMB (Dillard’s Store Card): Complete Dept. Store
Golden West Credit Union (Visa): Credit Union
HSBC (Orchard): Bank Credit Card
Kroger (1-2-3 CC): All Banks
Macy’s Store Card (mine): Dept & Variety Stores
Macy’s Visa (DH): Dept & Variety Stores
Well, that was a bit long - I"m feeling the need to Pepsi-up for my daily walk 
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Good luck to OP and whatever you decide to go for -- great score increases in the past few months – way to go!!!!