The TFSA versus RRSP question is usually presented as a rule. It is really a comparison, and the comparison is specific to you.
The core trade-off
An RRSP contribution may reduce your taxable income today, and the withdrawal is taxed later. A TFSA contribution gives no deduction, but growth and withdrawals are tax-free.
If your marginal tax rate today is meaningfully higher than it will be when you withdraw, the RRSP tends to win. If it is lower — early career, a low-income year, or a year of parental leave — the TFSA is usually the better home for the dollar.
What else changes the answer
Access matters. TFSA withdrawals are flexible and the room is restored the following calendar year. RRSP withdrawals are taxable and the room is gone permanently.
Employer matching usually outranks both. If a workplace plan matches contributions, that match is typically the highest-return dollar available to you.
Income-tested benefits matter too. Because TFSA withdrawals are not income, they do not affect benefits that are reduced as income rises.
A practical approach
Capture any employer match first. Clear high-interest debt next. Then compare your current and expected retirement marginal rates and split accordingly — many households reasonably use both accounts in the same year.
Run the comparison with your own numbers rather than a rule of thumb, and revisit it when your income changes materially.