In general, most people will be more comfortable waist training in an underbust style corset as these tend to be easier to fit, hide under clothing (stealth), and feel less restrictive than overbust styles. Apart from that, the corset should be sturdily made and a good match for the wearer's body. For some people with special fit needs, this may mean having a corset custom made, even if it's the very first corset they'll be wearing! This isn't the case for everyone though, and many people have no problem with beginning waist training in a properly fitted, off-the-rack corset. No single corset is going to work for everyone's body, personal preferences, or goals!
For people with curvier natural figures, or people who prefer a curvier corseted shape, corsets made in our hourglass silhouette can work well. For people who prefer a less dramatic shape overall or a more straight/conical rib shape, our gentle silhouette corsets may be a better choice. To cater to different body shapes and torso lengths we currently offer three different styles of underbust corsets (the waist cincher, underbust, and long underbust) for a total of 6 underbust corset variations to choose from. All of our corsets are made to a standard we believe will hold up to the rigors of waist training, hence the lifetime guarantee, so we recommend choosing something you really like the look AND fit of since you'll be spending quite a bit of time wearing it!
Keep in mind, waist training is a form of slow body modification. People's waist training goals, progress, and results are very personal and can vary wildly based on individual factors. What works well for one person may not work at all for another, so if you're just starting out you may need to experiment a bit to find what works best for you.