Question

difference between canonical form and standard form which form is preferable with gates?

Answer 1

The sum of minterms and the product of maxterms forms are known as the "Canonical forms" of a function.
F (a,b,c,d) = Σm(0,1,2,4,5,7) = Π M(3,6,8,9,10,11,12,13,14,15)
but "Standard form" is the expression itself ( AB+CD ) that you get from the canonical form, After using Karnaugh Maps (K-Maps) !
So you can design your circuit using the final expression !!!