It's been a while since I looked at Toodledo, so if any of this is incorrect, please accept my apologies in advance. :-)
Off the top of my head, some advantages would be:
- single-purchase vs. subscription payments
- being able to keep all of your data on devices you control if privacy is important. (No third-party server required, in other words.)
- all of OmniFocus' location-based features
- the ability to create and save custom views of your database (perspectives)
- Additional GTD support (the reviewing features, for example)
Other folks may have other ideas; hope this helps!