i don't feel like the twinsplit remix is very hard, actually it was the first trick i learned from the trilogy, but i'm not saying it's the easiest. the only other trick i really learned so far is the queens, i perform it regularly, i only use a slightly different production at the end (first i do what i think is called the houdini change, i then set the card down on the table which gives me just enough misdirection to tenkai the two face down queens on top and at the same time produce the second queen, and to finish i simply do a tenkai 2 card production).
as for the flourishes the easiest for me to learn was mecka, i also think ecko is not that hard, but i'm having troubles learning the tectonic thing and definetely the hardest one for me is pandora, but i suppose if you're doing a good tornado cut you can learn pandora quite fast as well, so i think it really depends on what you can do before you start the trilogy flourishes.