It really depends on your client. People with knee problems, obese clients and seniors often prefer the recumbent. I try to avoid bikes with most of my clients as they do enough spinal flexion and sitting during the day. I only have those who are really uncomfortable with other aerobic options use a bike.
using a bicycle is always my last choice, and I only use it when all the other pieces of equipment are taken and I am desperate for cardio.
Since I have a very poor relationship with bicycle seats, I tend to use the recumbent (but only kicking and screaming and with an eye on the other cardio options).