I’m AS 100k and DL platinum, I think Delta has better hard and soft product and on time performance is really good. However AS mileage program is way better. DL customer service outside of flying has gone downhill in last 2 years. Phone agents often more than useless. AS also not as good as before but still overall better.

My biggest issue with AS is basically cutting many transcon or mid haul routes. Great for west coast flying but otherwise meh.