【Sincere】 , 【wholehearted】 ,  【whole-souled】 ,  【heartfelt】 ,  【hearty】 ,  【unfeigned】  can mean genuine in feeling or expression or showing such genuineness.

【Sincere】 stresses the absence of hypocrisy, dissimulation, or falsification in any degree; it therefore usually connotes a strict adherence to truth, a revelation of just what one feels, thinks, or sees and no more, and an unwillingness to embellish, exaggerate, or make pretenses of any sort.

【Wholehearted】  and  【whole-souled】 imply the absence of all reservations and therefore stress not only sincerity, but also qualities (as earnestness or devotion or zealousness) which suggest that one’s whole being is stirred or moved.

【Heartfelt】 places the emphasis upon the depth and genuineness of the feeling which finds expression in words, in signs of emotion (as tears), or in acts; the term suggests that one is deeply stirred or moved, and it is applied usually to what might, by contrast, be formally or conventionally expressed or outwardly indicated.

【Hearty】  comes closer to  【wholehearted】  than to  【heartfelt】 , but it carries a stronger implication than  【wholehearted】 of vigor or energy in expression or manifestation, and may connote simple honesty, great warmth, or exuberance in the display of feeling.

【Unfeigned】  is often used in place of  【sincere】 , especially when the absence of simulation is to be stressed; the term usually emphasizes spontaneousness as well as genuineness.