At one time or another, I have used all three, because sometimes I don't want to alter the original connectors that came on a piece of gear (although sometimes I do, if the originals are no good), but MOSTLY I use bare wire, and I tend to prefer it. In a few cases, I use bananas, and only very rarely use spades (haven't done so for several months).
Bare wire theoretically gives the best connection (fewest interfaces at which the signal might degrade), so these days I tend to use it, even with connections where you could use a spade. I always try to imagine the "flow of electrons" in the wire when putting a thick, multi-strand wire into a narrower socket, and allow for maximum contact/flow. I've thought of using those needle-like insertable things that clamp onto the wires, but haven't tried them yet, so for now I use mostly bare wire.
Bananas

have the advantage of being the quickest and easiest to insert and remove (Oooh, maybe I should re-word that?

), but probably don't give the best contact/connection, especially if you leave them in after a while. Some of the newer banana plugs work better (tighter fit, larger connection area, still easy to remove). When I'm playing around with combinations of gear (swapping things around just to hear them), I'll usually test them with bananas first. If I intend to leave something hooked up for a while, I'll switch over to bare wire, if the connector type allows it.
Especially with bananas and spades, remember to periodically clean the connections with DeOxit. Maybe not necessary if all surfaces are gold-plated (?), but otherwise corrosion will build up at speaker-wire connections just as it does with control pots, relays, etc... Once a year is a good rule of thumb for this, but it may vary with your environmental circumstances.