Given the choice between a flattened and stored bike box being reconstructed, or putting a bike in a large plastic bag for a return trip, which would (or have) you choose(n)?

I've got the option of doing either this trip. Transport and store the box in a flattened state, to use on return, or just show up at the airport, buy the plastic bag for $15ish, and turn handlebars but otherwise put bike in completely assembled and be done with it. I'm mostly worried about how effective the bottom of bike boxes are once the staples have been pulled and it is just tape holding it together.

Leaning towards bag, just for convenience, and I don't foresee any damage that can't easily be fixed at home anyhow. More touchy about the bikes on the way there.