RE: one or all three
#1 what are you traiing for, fitness, speed, fighting, or fat-loss?
#2 what kind of bike, road/mountain or indoor[stationary]?
#3 utilise as much different cario as you can as a general rule
#4 with the exception of that TL gazelle thing, if it is, what i think it is, [as seen on TV] it is a useless pile of sh1t unless you are useing it to recover from an injury and need a low/none impact exersize. sorry if that sounded harsh.