While DL has improved greatly I still find it impossible to book an award. I have been trying to burn 150K miles with them, unable too. Even though CO has been called NonePass I still find it easier to use.

Upgrades depend on the routes you fly really. As Plat on CO I've been very successful. Gold on DL I have been happy with percentages.

I am used to CO and find them my preferred carrier all around. I have also gotten used to EWR for a NY airport. Not happy with customer service at EWR.
I am really happy with my Chase Presidents Plus MC.