Tasks: iPad wins (uncontested)
Apple's Reminders app is not special -- let's be honest about that. You can do the basics: Create tasks (including repeating ones), set task priorities, set which task list they belong to, and reorder items within its list. Tasks can also be synced via iCloud and/or Exchange accounts.
But you can't see a unified view of all your tasks across accounts, and you don't get that neat location-tied reminder capability that Reminders has on the iPhone.
However, there is no tasks app, or capability for tasks in another app, in Metro. You have to use the full Outlook app instead (an optional purchase in Windows 8, but included in RT), which is not so easy on a touchscreen device.