Newfoundland
Jeez, I hope you don't make this decision based on car rental availability?
My (Canuck) vote goes to Newfoundland. Both provinces require a lot of travel, but NFLD. is more rewarding - the people, customs, landscape & accents.
Once you decide, share more details of your proposed itinerary, airports, likes/dislikes, etc. and we can share more ideas & suggestions.