As to your question of which kind of tickets are "best" (and assuming you aren't talking First or Business class) - if you know your dates won't change, go for the cheapest possible. Within a given fare class, they'll generally get you into the same seats on the aircraft. But if there's a real chance that they may change, you may be better off with a refundable fare. The latter is more expensive up front, of course, but may save you money in situations like these. The key is reading the terms of each fare, seeing what the penalties are for changing, and deciding which best meets your needs.