Ribbons generally give a much more transparent and spacious sound stage. They are also less efficient.
They work a lot like electrostats, on a smaller scale. I have a pair of Carver Amazing Loudspeakers (version III). The ribbons are 48" tall, giving that open. spacious, non-directional sound:
They radiate front AND REAR, which helps give them that spacious feeling & presence. They really must be heard to understand.
Horns can be shrill if not properly managed (quality crossovers & amps), but almost always provide more "impact"...IMHO. Each have their strengths; it's mostly a personal preference. I have both and enjoy each for different reasons.