Best travel rewards for small local municipal airport with limited options

My closest airport is teeny, so we don’t have many options flight wise. We usually fly Alaska (already have this card)and Delta, and sometimes American and United.

I tried to apply for a business Delta Sky Miles Reserve and they are asking for my tax records. I filled out the form and sent it in. Called to check on it and they said the form was wrong and missing info. No notification that there was a problem. Turns out the form THEY SENT had the bottom portion missing. When I call, it’s a bunch of scripted plebs that offer little to no help. Ready to ditch this and try elsewhere because I’ve wasted too much time already. But maybe I should stick with it or apply for a personal card?

I travel 5-6x times a year both domestic and international. For business and personal. My son may be going to college in the UK, so this will likely increase. I would like lounge and upgrade options.

Credit score 820+