According to the following ngram, "tons of" is the most common:

Source: Google Ngram

Yes, they are interchangeable, but here's how I usually use them:

A ton of: countable objects.

Tons of: uncountable objects.

Such-and-so candidate for mayor has tons of charm, but is a little light on the issues. Explanation: charm isn't countable.

She's already got a ton of stuffed animals, let's get her something else for her birthday. Explanation: the stuffed animals are countable.

(Yes, you could also say tons of stuffed animals.)

The use of "tons of something" by LONGMAN Dictionary is given in URL.

tons of "something"

https://www.ldoceonline.com/dictionary/tons-of-something

Therefore, the phrase of "tons of ..." also supports both countable plural noun and uncountable singular noun.