If you're just starting out your fitness regimen or aren't interested in an advanced machine with many complex features, these elliptical trainers are right for you. These machines are more light weight and have a few basic programs, so you can start to get a basic cardio workout in the comfort of your home.
If you've been training for a while and need a machine that has more workout options and will allow you to push your limits, you will want an elliptical with more features. These machines are capable of bearing greater weight, can remember settings for multiple users, and have heavier flywheels and larger brakes, resulting in a smoother workout.
These ellipticals have all of the features a long-term fitness enthusiast will need. These machines are made with heavier materials and come with a greater variety of preset and custom programs for a complete fitness regimen. They have heavy-duty back flywheels like models found in gyms, and lots of programs so you can vary your workout as you get into better shape.
Prices vary, but simply put - spend more, get more. Exercise bikes fall into 2 price ranges: Over $500 for a smoother, sturdier ride with better resistance, more adjustability & features. Under $500 for lighter use. You'll still get a good workout, but less bells & whistles.
You have 2 choices: Uprights resemble usual bikes & have less lumbar support, but make for intense workouts. In recumbents, you're reclined, with back support & feet in front - comfortable & ergonomically correct, great for someone with back problems or new to exercising.
Fitness goals are crucial to your choice. A $500+ bike is great for intense cardio, but it doesn't mean a pricey bike isn't ideal for novices. If you want to exercise often, quality bikes can convince you to keep it up. For modest goals or light use, look for a bike under $500.
Important features to consider: Resistance, this is what makes your workout challenging. Options include Belt & Fan, Magnetic & Range. Other features to keep in mind: Adjustability (to ensure you'll fit properly); Display & Monitors (so you can keep an eye on your progress).