Bare wire oxidises and loses contact, and poor quality bananas work loose with time. Use single piece bananas (not the ones with the leaf spring contacts on the end) or an expanding type for best long-term fit. Spades offer the best electrical connection and are totally gas-tight, I would use them where long-term stability is a concern. Speaker pins also work very well when used in the slot where bare wire would go.
Crimped connections are better than solder, but normally speaker cables have a large number of very thin strands so crimping may damage the wire and cause loose contact over time. I just prefer solder.
Bare wire should be used only when there is no option of using bananas (solid center posts) and quality spades are not available. Be sure to tighten connections once a few months, and clean off the the wire ends when doing this.
This is not about sound quality (not directly) you are looking at a connection that is airtight and stays locked down. If you don't plan to move your speakers around or change connections very often, bare wire will work fine as long as your binding post ensures it does not work loose. Most posts I've seen require retightening, and oxidise the wire even at the contact point (=not gas-tight).
