This whole sizing thing is, to some degree, a lot of nonsense. Like a2psyklnut says, you have to ride to see what is comfortable for you, and you alone. Most bikes have (fairly obvious) at least three frame sizes: S, M, and L. The geometry of the frame is usually identical, and in the most part the only difference is to be found in the tube lengths and the angles are the same. In that case, bike A will be ideal for only a % of people, bike B for another %, and so on. That's why you need to ride some different types. Sure, you can make some adjustments, like seat height, seat angle, how far forward or back the seat is, bar width, bar angle, bar height, and other things. Some bikes have different head tube angles, and that can make a difference, but whether the average rider can deduce that, or even care about it, is another matter.
Don't overlook brand loyalty either. Most folk are polarised and will only buy from one manufacturer or by suggestion, reason, or emotion, will exclude some brands so you will select from the choices remaining. Nothing wrong with that. What you are prepared to pay, prepared to listen to, prepared to read about, prepared to talk about will ultimately point you in the direction of that you can select from. At that point, sizing will be secondary.