This really depends on what you’re hoping to achieve. For people who want a road bike trainer to train specifically for cycling, an indoor trainer is the better option.
Indoor trainers mimic the feeling of riding an actual bike while riding on a stationary bike stand. They can simulate the hills, sprints, and even road textures that riding outside entails.
Indoor trainers also let you use your own bike, so you’ll be more prepared to ride outside when the weather clears up. They’re also lighter and more portable, so you can store them when they’re not in use.
If your goal is to get in shape and you aren’t necessarily concerned with your cycling performance, a stationary bike is a great option. They’re generally quieter, they don’t require you to use their own bike, and there’s no setup required after the initial setup: it’s always ready to ride.
They take up more space, however, so if you don’t have a spot in your house specifically for working out, this may not be the option for you.