Can I file jointly with my wife using the free edition, or do I need to purchase the $39.99 version? If so is there an an easy way to tell which filing type is best?

Many married couples are able to use the TurboTax Free Edition.  Which edition is best for you depends on your personal financial situation.  Here is a link to our Products & Pricing and you can check the boxes for the situations that apply to you and TurboTax will recommend the best product.  Products & Pricing for TurboTax Online

Generally, filing jointly will give you a bigger refund or less taxes due.  When you file separately, your tax rate is higher and there are several credits you cannot claim.  Please see the TurboTax FAQ below for more details:

https://ttlc.intuit.com/replies/3288477

I didn't see the ability to file jointly using the free version, did I miss something in the first few pages?

Here are the steps to get to your personal info and choose your filing status.  Select My Info (in left column of page). You will see your Personal info summary and below the first name on the return, you will see your filing status. Click on the Pencil icon to change your relationship/filing status.  Let me know if that works.