Which sentence uses the correct form of interesting to make a comparison?

that's the most interestingest book i've ever read.

that's the most interesting book i've ever read.

that's the interestingest book i've ever read.

that's the more interesting book i've ever read.

That's the most interesting book I've ever read. (second option)

Explanation:

The sentence requires the superlative degree of the adjective describing the noun 'book'.

The adjective interesting forms its superlative degree by placing 'most' before the positive form: the most interesting.

glamis thou art, and cawdor; and shalt be what thou art promis'd; yet do i fear thy nature; it is too full o' the milk of human kindness to catch the nearest way: thou wouldst be great; art not without ambition; but without the illness should attend it. what thou wouldst highly, that wouldst thou holily; wouldst not play false, and yet wouldst wrongly win: thou'dst have, great glamis, that which cries, "thus thou must do, if thou have it: and that which rather thou dost fear to do than wishest should be undone." hie thee hither, that i may pour my spirits in thine ear; and chastise with the valor of my tongue all that impedes thee from the golden round, which fate and metaphysical aid doth seem to have thee crown'd withal.  

he lacks ambition.  

he is hesitant.  

he lacks courage.  

he has moral scruples.