Which sync method should I use?

Dropbox is the recommended sync method for 2Do. It's supported on iPhone, iPad, Mac, and Android, and it carries every task property — including List Groups, Tag Groups, Smart Lists, attachments, and Search Presets.

• Dropbox — recommended; full feature support.
• iCloud CalDAV — useful for Apple-hosted CalDAV sync, but does not sync List Groups, Tag Groups, or Smart Lists. It can sync a maximum of one picture and one audio recording per task.
• Custom CalDAV — Fruux, Yahoo!, ownCloud, Synology, and other CalDAV servers. Same limitations as iCloud CalDAV.
• Toodledo — useful if you already use Toodledo's web client. Manual sync only on iOS; some features don't map. See: Sync overview (iOS), Sync overview (Mac), Sync overview (Android).