No credit card required
Browse credit cards from a variety of issuers to see if there's a better card for you.
Is attempting both not an option for you at this time? I'm not exactly up-to-date on NFCU rules regarding apps and CLIs but seems like if you're undecided why not both. For a possible increase on your goRewards a HP is nothing really in the grand scheme of things and since you're already prepared to take a HP for a new account I don't see the issue with Flagship app either. If I had to choose between the two I'd go the CLI request route because if you put any kind of spend on it there's more of a likelihood of an increase.
I will say I am surprised on the denial reason considering your signature and the cards you currrently have.
Since you're past the 91/3 I would go ahead and apply for the 2nd card, if the Flagship looks good to you, I would bet you would get it this time around.
I would honestly hold off on the CLI for the 181/6 time frame...you may get it if you apply now, may not..I tried at over 3 months and was denied, and tried again @ 6 months and got a 4k bump on one card and a 7k bump on my 2nd card.