Welcome back! Thought you were gone.
Personally I use 720p(1280, 720) as my target resolution. If I need to scale down it's not that much or if I need to scale up it's not that far either.
Even though a lot of phones/tables have super high resolutions there are still a TON that don't and aren't super powerful. I'm using a few layer shaders that work fine at 720p but they'd probably really chugg on a resolution higher than 1080P on a midline phone.
That's my two bits at least.