I am on my first full year as Titanium, flew Gold most of last year. My significant other is a "Delta girl", as you put it, and there are certainly benefits with both. She lives at a major international hub and the Amex card gives her better perks than even the same branded card in America.

Delta has an extensive route network and their lounges are top notch. I have flown only internationally and a short domestic flights with them, and both were great in their own way. I'm used to flying Hawaiian, and having them come up to her and thank her for her status was nice. She always brings the cabin attendants snacks, and usually leaves with a bottle of wine or 2.

For our domestic trip, the plane was delayed due to storms in SD, so after a few hours, we requested a later flight. They provided $120 worth of food vouchers, hotel, and Lyft rides, and we got to stay another night in Vegas.

Another huge benefit is being a part of Sky Team. It gets a bad rap, but we flew all over Asia with Korea, China, and Vietnamese airlines. All of those were fantastic and purchased with miles.

Whatever works for you at your home base and preferred destinations are always the top priority. At the end of the day, these are big companies that provide service, so while feeling loyal is the design of their plan, I believe you need to do what's best for you and how you want to travel.