Which is more beneficial to your bottom-line (disregarding the cost associated with actually getting married, and assuming no children are involved).
The areas most people benefit from are:
- Pooling resources: for income tax there really is no advantage to marriage over common-law status. All the same deductions are available.
- Sharing health and dental benefits: there is no special status associated with marriage over common-law
Income Splitting would be a benefit that is currently not available in Canada. It is currently available in the United States, although I am not sure if it is offered to common-law as well as married couples.
The benefit of marriage vs. common-law is typically in succession handling. The nature of common-law allows for the possibility of multiple concurrent spouses i.e. if there is a dishonest individual there could be several common-law spouses at the same time. In the event of no will then it would be the first claim to be settled that would be addressed. However the possibility still exists that a second claim could come forward to contest the estate. Then it would be for the courts to decide. A marriage contract is more legally binding since it excludes all others (one can only be married to one person serially at a time in Canada).