Answer: The main clause is "Cats make good house pets".
Explanation: The main clause is the clause that can stand alone as a sentence. In that way, in a complex sentence, the main clause is the independent clause since, unlike a dependent clause, it expresses a complete thought. In the sentence provided, "Cats make good house pets" is an independent clause and the main clause because, unlike "although I like snakes better, it expresses a full idea and it can stand alone as a sentence.