I have owned exercise bikes, treadmills, rowing machines... and eventually they just stop getting used. And then at last they get sold or given away.
So I would say, use the Gazelle you have... but if you can't face that and just need some variety, consider a gym membership. You'll find many people at the gym are in the same boat as you--and you'll have lots of different machines to work with. Prices vary a lot, so shop around. Avoid contracts.
As for exercise bikes, the best one is the one you'll use. Shop around for these, too, if you just can't face a gym. Different style work for different people--I am uncomfortable on a recumbent-style bike, for instance, and prefer an upright one.