Portugal has three operators, Vodafone and MEO have very good network coverage, NOS is less-than-stellar. Similar to comparing AT&T and T-Mobile in the US, not recommended when traveling around less-populated areas of the country. Vodafone is good in Denmark as well.
The vodafone booth in the T1 arrivals hall is open everyday from 7 am to 8pm. The airside stores have varying and reduced opening hours.
They'll sell you a SIM card with 5 GB of data and 500 voice minutes /SMS good for four weeks for EUR 10, and you can adjust that according to your needs with more or less data and minutes as you please:https://www.vodafone.pt/telemoveis/tarifarios/you.html