I've found bootlace crimps to be a tidy and long-lasting solution, and I doubt they degrade the connection in any significant way. Seeing as it is the standard in electrical installations, I am sure it is a reliable connection, at least for screw terminals. They can be moved side-to-side in some spring terminals, but seem to make a good electrical connection nonetheless and cannot be pulled out easily.
That said, bare twisted copper wire has served me well for a long time in screw terminals or spring terminals. If the end ever starts to get too shabby, it's easy enough to cut it off and strip another length. I've also used tinned/soldered ends before, the main trouble is that the wire has a tendency to fray and break near the end of the tinned section, as the tinned portion has no flexibility, and after a few times in and out of screw or spring terminals these can still get quite out of shape anyway. As a result, I don't tend to use this method any more.
If I'm permanently attaching wire to a connector, though, even if it has a screw terminal, I prefer to solder it. More reliable and neater, in my experience. I recommend supporting the wire with some heatshrink to prevent it breaking near the connector.