From The Collaborative International Dictionary of English v.0.48 :
Preferable \Pref"er*a*ble\, a. [Cf. F. pr['e]f['e]rable.]
Worthy to be preferred or chosen before something else; more
desirable; as, a preferable scheme. --Addison.
[1913 Webster]
From WordNet (r) 3.0 (2006) :
preferable
adj 1: more desirable than another; "coffee is preferable to
tea"; "Danny's preferred name is `Dan'" [syn:
preferable, preferred]