I currently have an SPG Amex and a Merrill+ card, and I'm looking for a third.

I want a third card for two reasons: I want to have a backup card that I'll rarely/never touch besides my two everyday cards, and I want to increase my ratio of unused credit to total credit for credit score purposes.

I am not looking to churn. I'm looking for a good long-term card, and I value good customer service (and will pay a little accordingly).

My spending profile is in transition right now, but I expect to be spending quite a bit on the following in the near future: rent (can I put that on a card?), air travel, hotels, food (probably a bit more restaurants than groceries; workplace provides much of my meals), electronics; and probably in that order.

I currently put everything on SPG, and only use Merrill+ where Amex is not accepted, and I tend to stay Sheratons (Starwood) most of the time (one hotel in particular, in fact).

Now Amex, for some reason, didn't approve my credit line increase, so my secondary card will likely still be seeing some spend. Because I don't fly a particular airline frequently, I'm considering a Citi PremierPass (maybe Elite) to be my second everyday card, and pushing Merrill+ to be my don't-touch backup card.

Thoughts/feedback? (Any information that would be helpful to you that I didn't include?)