assalamu alaikum ustadh,i have a question about how do we choose b/w diff fatwas and rulings. for example sheikh salih al fawzan said we shorten prayer when our journey is less than 4 days . but i studied in one of ur lessons the view of ibn taymiah that when one is "travelling", he shortens even >4

Look at the evidence first, because every fatwa is built on the Qur'an and the Sunnah, and what the evidence supports is what is followed in a matter of disagreement. If the two are equal to you and you truly cannot tell, then take from the one whose knowledge and religion you trust more. As for the matter in hand, there is no clear cut evidence deciding the time, thus it is open.