Hi Antonio,
As it’s hard to compare between these two options. I’ll give you some of my knowledge about the north and the south area of Myanmar to compare. 
– The North direction:
Because of conflict problem in the past, there’re some additional travel restrictions (such as blocking land or water routes to Myitkyina) in this area of Myanmar.  However, those parts are safe to spend time with local people. One way to do this is to take a boat trip on the  Ayeyarwady River north of Mandalay around Katha and Bhamo, where long journey times and a scarcity of foreigners make it easy to get a sense of provincial life. Heading northeast from Mandalay instead, towards the Chinese border, treks from towns such as Hsipaw into the forested interior offer up the opportunity to stay in ethnic minority homes in traditional mountain villages.
– The South direction:
Late in 2013 the travel restrictions were relaxed, and it’s now possible to travel as far south as Myeik overland. Southern Myanmar stretches from Hpa-an in the north to Kawthaung in the south, it is a lush a vibrant area with much to offer those who travel south.
While the Myeik Archipelago may be Tanintharyi’s main draw, the coastline around Dawei is the surprise star.  Fishing villages spill right down to the gloriously clear water at San Hlan and elsewhere, a lone golden stupa looks out over the Andaman Sea at Shin Maw, and dirt tracks lead to gorgeous stretches of sand everywhere. 
Hope you have a nice trip in this beautiful country