Seems like there's a never endless number of to-do apps. I do like the interactive demo on TeuxDeux's homepage. Slick.

teuxdeux looks amaze but for me personally i ended up with a mix of quip and any.do

I'm still old skool with Remember The Milk...their prioritization feature is a must for me, something I haven't found in any other (compelling) task management apps.

Things.app for life.

I'm still using clear but know several people that swear by TeuxDeux. @destroytoday out of Studiomates is who you can follow for updates and tips/tricks.