[pref-er-uh-buh l, pref-ruh- or, often, pri-fur-]
worthy to be preferred.
Origin of preferable
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
preferred or more desirable
Since preferable already means more desirable, one should not say something is more preferable or most preferable
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
1640s, from or on model of French préférable, from préfér (see prefer). OED notes preferrable is better English but has not prevailed. Related: Preferably.
Online Etymology Dictionary, © 2010 Douglas Harper