I would really say that it depends on what you plan to use it for. If you are only going to use the treadmill to walk, then why not go outside and walk (unless you have a little one that is sleeping and you are using that time).
A bike is better than nothing, but unless you are really exerting yourself I find it very hard to believe that you would burn more calories than walking. Walking is weight bearing exercise, a bike is not, therefore walking (or running) is better for you IMO.
I would definitely go the treadmill. Just my views though.[i][font=Trebuchet MS]Trying for our first!!
(since March 04)