Every Mahjong player seems to have a board style they prefer, and the degree of difficulty may have nothing to do with it. Diamond Mine is one of the easiest games for some people, and yet others consider it very hard. While you would consider Basic to be the easier game, there are players who seldom clear all the tiles.
Most players consider the Pyramid style the hardest of the Mahjong games. This is because of the limited number of tiles available at any one time to select from. The only way to know for yourself is to play games among the different layouts and see which you like best.
You will no doubt find one game that you like more than the others, but adding some variety makes it more challenging and new. If you try one board four or five times and cannot complete it, switch to another one and come back to the one you had a problem with later.
Experience makes you a better Mahjong player. Don't be discouraged if you don't win each time you play. It is not to be expected to always complete the game, and if it was so easy to do, you wouldn't enjoy the game as much. You will improve at the game of Mahjong if you play it more often.