i am giving exams in IDTA i only know istd is there a diference in american style ?
which is better
my instructor tells me that in american style latin it is better than istd !
can someone tell me ?

Better ?-- moot point-

it depends very much on your location. If you are in the States, there is far more opportunity, to dance what you learn , with a greater number of people.

The english equivalent, has many similarities , and again, depending on whether you choose social and or the more competitive style , could affect your usage ( if no partner )

They, both styles, may be danced in competition . Again-- decide the path, you wish to persue .
The bronze american style rhythm, has more dance variety from which to choose .
Mambo-- salsa --rumba-- bolero-- cha cha-- samba-- west coast swing -- east coast swing-- merengue-- hustle .
The availibility , of a teacher close at hand, might determine your choice .

As far as actual differences are concerned , too many to list here . essentially, the concepts are the same. The approach may differ in certain dances .