tldr: he used a basilisk because that was the best option available to him
This answer is based on the assumption that all the information we have about Slytherin are correct. I also recommend you to read and upvote this as it's a good answer. But I also think it's just a theory, and as more new material gets added to the Harry Potter universe, I think we ...
In addition to the excellent information in Bellatrix's answer, I want to add a few more details that we know: (all non-book quotes are from the Chamber of Secrets article on Pottermore)
Salazar Slytherin had a grandiose opinion about his importance to the school:
However, it is clear by the very decoration of the Chamber that by the time ...
Salazar’s reason is never truly confirmed.
It isn’t known for certain why Salazar Slytherin put the basilisk in the Chamber of Secrets. Though the often-cited explanation is that he did it so he or one of his descendants could rid the school of all those who were unworthy of studying magic, it’s unclear if this is proven anywhere or if it’s just a ...
There’s some information, but few details.
The exact details of everything that happened leading up to Salazar Slytherin leaving Hogwarts aren’t all known, but in Harry’s fifth year, the Sorting Hat tells a bit more about it.
“And never did they dream that they
Might some day be divided,
For were there such friends anywhere
As Slytherin and ...