Although technically Best Press is "in the starch family", in reality it acts much more like sizing than like starch. If you buy a can of spray sizing and use that on fabric, the result will be very similar to Best Press. Sizing is man-made from chemicals and used in garments to add just a light touch of body (e.g., for collars and cuffs) without uncomfortable stiffness.
Starches (other than Best Press) are derived directly from organics -- rice starch, potato starch, cornstarch, etc. You can make your own starch at home from cornstarch, for example. Commercial starches are sold with preservatives so they last longer after mixing with water. Starch can be made very strong or in a weaker dilution, depending on how stiff you want the fabric to become. For heavy starching, I mix 1 part Sta-Flo with 1 part water. This adds a lot of stability to fabric. Muslin, for example, comes out as stiff as a lightweight cardstock.
I think that Best Press is classified as "in the starch family" because of the alcohol content. In the home recipe, for example, the alcohol used is vodka (very high percentage of alcohol) which is made from grain. Although the source may be ultimately organic, the end result is much closer to a sizing.
What you use depends on what you are trying to achieve. If you are looking to add lots of stability to fabric, you will probably be unsatisfied with sizing and Best Press.