Will I receive a 30-day visa upon arrival in Thailand after traveling to Vietnam, or do I need to apply for a 60-day tourist visa?

You don't need a visa if you are visa exempt, as you will leave the country after a week or 2, then only be in country the 2nd time for less than the 45 days again. (I believe the 45 day exemption ends on March 31st. If not, you can still get the 30 day extension.)

So you will get 45 days when you land, when you leave and re enter Thailand you will receive a new 45 day stamp. If needed you can go to immigration before it runs out and extend it by 30 days. (this is assuming you are from a visa exempt country)

Re entry issues you may see asked often in this group concern long stay people who take advantage of tourist visas and border runs to live in Thailand long term. If you're here less than 6 months it's unlikely to be an issue.

Tourist visa 60 days is single entry so I wouldn’t do that, until May you get 45 days visa exempt so you should be fine.

I’m going on the assumption you come from a country that is visa exempt, your name sounds Dutch 😉)

What is your nationality?