No credit card required
Browse credit cards from a variety of issuers to see if there's a better card for you.
With three open accounts, you want to pay TWO of them to zero BEFORE the statement cuts.
Let the third card cut with a small balance. (less than 9% of THAT CARDS limit.)
That will maximize your score from the utilization perspective.
Depends on what you mean by boost. What kind of boost are you looking for? What's your cards, limits, and balances? Do you have loans? Derogatory marks? What are you trying to do that needs a quick boost?

I would suggest getting the shared secured loan technique for the credit mix and will give you a good boost. Then I would not app at least 1 year from your newest card. You can request credit limit increases, as long as they are only soft pulls against your credit reports, and make sure they are open at least 6 mos.
@Anonymous
Scores (Fico) TU: 677 EQ: 670 : EX: 690
Something sounds off to me. With 19% utilization (aggregate) and no negative items on your CR, there's absolutely no reason you shouldn't be at > 700 scores. Someone with 6 months of credit history and just a couple of accounts with low utilization and no negative items will debut with a FICO score of 720-730 quite often. I'm not sure what the disconnect is here, but I'd look into it and address whatever it is.
Another thing I'd suggest OP is closing some credit cards that you don't use. If you have 9 cards and overall limits of ~$15k, your ACL (average credit limit) is quite low, which isn't a very favorable look. This can very well be a constraint to account growth as well as a constraint to obtaining a nice SL on a new account. If I were you I'd close down any cards that you don't use at least every month or two and then go for SP CLIs on all of the others in attempt to raise your ACL.
Is Alliant still giving shared secured loan? I was thinking of applying for one.
OP - You can check out this thread.