I've been playing them a lot recently apart from super star saga because I only have a 3DS but they are all good games, which is your favourite? I HAVE CHORTLES !!!!!!
I'd say... Super Mario RPG, where Geno makes his first appearance. Geno is one of a few Mario Characters that I like in terms of usefulness, story, etc., to be honest.
Ooh... we're doing one of these! Well, kids, I'd have to say that I like Superstar Saga, where Cackletta of the BeanBean Kingdom and Fawful, presumably of the BeanBean Kingdom, as well, makes their appearance as the main antagonists. By the way, I HAVE CHORTLES!
Definite favorites have to be Paper Mario The Thousand Year Door, the first paper mario for n64 which you can play on virtual console for Wii U, mario and luigi superstar saga, mario and luigi bowser's inside story and mario and luigi partners in time.