This really depends on your goal and financial situation. Do you want a refund? Do you want to break even? If you both claim exemptions and married you may end up having too little withheld.
You can use the TurboTax Calculator built into the program that already has all of your information to help you figure out the best way to fill in your W4 so you don't end up owing.
To access this calculator, click on
You can also use the TurboTax W-4 Calculator at the following link. https://turbotax.intuit.com/tax-tools/calculators/w4/
Allowances/exemptions no longer exist on tax returns or the forms W4. Withholding is now a factor of your income and deductions/credits. Here is the IRS W4 Calculator to assist in creating a new W4 for your employer.