If your thinking about which is easier its really personal preference, some people are better at one than the other.
With Double Battling positioning of the Pokemon is meaningless while in Triples the middle Pokemon will be able to attack all Pokemon on the foe's side and on its own side, at the cost of in return being able to be attacked by every other Pokemon on the field. The Pokemon on the left and right sides will only be able to attack the Pokemon directly in front, to the side or diagonally to them. I like to think of triple battles as two double battles at the same time with an overlapping Pokemon in the middle ^_^
Some abilities like Intimidate are also affected like the Pokemon moves. Also there's more to process in triple battles and it's not as popular as Doubles.
So Doubles is technically easier, there's less to process and it is easier to make up combinations as well.