Delta is amazing, upgrades are top notch, getting to have lounge access at gold is great, as is the bags (which they are slowly moving towards making one free anyways and dropping change fees).
I've never really had a bad experience on Delta at all, and I literally fly it exclusive internationally. Domestic is still got some SWA mixed in but depending domestic Delta is hard to beat (for me).
Can't imagine doing United or AA, just
Once I start up my Canada travel again soon it's going to racking up a lot of miles again which I'm am going to be happy for.