I'm going out on a limb here, i'm going to say Tobiano, with some Sabino.
I always thought of the color patterns in this way, Tobiano-white crosses the back
Overo-white does not cross the back between withers and tail.
Sabino-jagged/lacy edges on spots
Splash-is mainly occurring from the belly/barrel, as the color stays on his top line.
I'm far from an expert. So now i'll wait to see how far i'm off.
Good luck!! Nice looking horse btw!!!