What is the correct (or best) oil to use for fondue?
Assuming this is a meat fondue (AKA fondue bourguignonne), using oil instead of cheese:
There is no best or correct oil to use - each type of oil has its own characteristic flavour. However, a meat fondue generally involves heating the oil to 350-400° F (175-200° C), so you'll want to treat this more or less like deep-frying and use an oil with a relatively high smoke point.
That means, no unrefined olive oil, sesame oil or walnut oil, and be extra careful if you want to use butter (clarify it first). Canola, sunflower, peanut, grapeseed, etc. are all good choices, or any of the refined versions of olive/sesame/walnut with higher smoke points.
Personally I'd either use refined olive oil or a flavour-neutral oil like peanut or sunflower. Most of the time you don't want to be imparting any "foreign" flavours to meat, although I suppose you could go with refined sesame oil for a moderate Asian twist.
I personally use peanut oil or canola oil. Like Aaronut mentions, some oils will add a mild flavor to your meat, so keep it in mind when choosing. I find canola to be the "tasteless" oil in the sense that it doesn't add any flavor. Peanut does to a certain extent, and so does olive oil... I would choose the oil in combination with your fondue dips (you should have at least 3 of them, to dunk the cooked meat into).