Just adding to this run in conversation (because i too am having the dilemma and my efforts making my own version in CI got me close before time put a stop to that!)
I have run through and top runners do seem for me:
Active Collab - Paid for version, although it is an expense to pay to include time tracking $400ish, and license only valid for current major version.
Basecamp - Again an expense to pay - especially for plugins, addons, and more clients / projects.
Project Pier (Activecollab 0.7 fork) - Ideal, but no time tracking, which i ideally want.
OpenGoo (AC 0.7 Fork) - Exactly as ProjectPier, but with extra bits like time tracking. But somehow the information, especially the dashboard did not present the information i wanted / needed… But for those who wanted it… it does have multi-level task lists, as many as you want i think.
And now… just running out of ideas, getting tired, feeling a headache coming on, and the full active collab is looking might suitable right now!