I saw an article addressing which was better the bike or treadmill for cardio. I only scanned the article (which did make some good points), because the answer is simple: which every ergometer you will use.
Sure, there are some differences, e.g., cost (treadmills $$$), space requirements (stationary bikes—i.e., leg ergometers—take up much less space), calories burned (treadmills might have the edge here), muscles used (bikes may have greater benefit for leg muscle hypertrophy), comfort (bike seats chafe), etc.—but, in the long run, it comes down to which you prefer (and which you will use regularly). After all, any exercise that is not performed is not beneficial, and any activity done is better than that which is undone.
What cardio equipment—treadmill, bike, stepper, elliptical, rower, etc.—you use will largely depend of availability. If you are buying for home, it will be a matter of budget and space. Don’t skimp on the budget. Buy quality. Buy used, if you want to save money. (We had a used Tectrix Climbmax for at least 12 maintenance-free years that we bought used. It was a great investment.) Whatever you buy, be sure you will use it. Too many quality pieces of home exercise equipment are left to collect dust. If you are going to buy it, use it!
If the budget is really tight, there is always outdoor running/walking—or dusting off the old road bike. Another option is a Daily Burn (or the like) subscription. Just do something.
Not sure what to do with the equipment? There are plenty of free videos on YouTube or interval or HIIT workouts. Clamp an iPad holder on the stationary cycle and pedal along to a workout video or to your latest Netflix binge. Just start exercising. No excuses.
Be your best today; be better tomorrow.
Carpe momento!