which Update quicker

Hello list,

For a big table with more than 1,000,000 records, may I know which
update is quicker please?

(1) update t1
set c1 = a.c1
from a
where pk and
t1.c1 <> a.c1;
......
update t1
set c_N = a.c_N
from a
where pk and
t1.c_N <> a.c_N;

(2) update t1
set c1 = a.c1 ,
c2 = a.c2,
...
c_N = a.c_N
from a
where pk AND
( t1.c1 <> a.c1 OR t1.c2 <> a.c2..... t1.c_N <> a.c_N)

Or other quicker way for update action?

Thank you
Emi