I have noticed there are many ways to get the "should" idea across and was wondering what is the most used form? ie -meli/-malı, zorunda, gerekmek etc

Many posts on this subject. I struggle with this too. It depends on the context. Try these:

http://www.turkishclass.com/columns/alameda/2009/forumTitle_2708_2

http://www.turkishclass.com/turkish_lesson_178

http://www.turkishclass.com/turkish_lesson_77

Or insert ´Must´ in the search box top of the page.

Thank you so much I´ll check those out!