Milotic by far.
I think Gyarados is kinda ugly.
Because it's based on a Japanese myth about a carp that turns into a flying sea serpent or something.
Chinese myth. Don't say anything that you aren't 100% sure of.
The myth said that there's a gate called 'the dragon gate' in East China Sea. When a carp hops over it (you see, Magikarps hop really high when splashing), it turns into a dragon, a typical Chinese Dragon that doesn't breathe fire but water instead.
Gyarados should be Water/Dragon, but in order to keep the rarity of Dragonite, Charizard, Seadra, Rhydon and Gyarados are all sacrificed. In the next generations, Seadra eventually gained a second type of Dragon by evolving into Kingdra, and Rhydon evolved into a very fearsome pokemon. In the 3rd gen, dragon type became no longer 'noble', likes of Altaria also appeared. Unfortunately, Gyarados and Charizard are forever sacrificed because of a BL semi-legendary!
I think Gyarados's typing is fantastic though. Nearly all rock moves are weakened by Intimidate, and a Lightning-rod partner helps Gyarados to get rid of electric moves in double battles.
Also, Gyarados looks much cooler than Milotic. Milotic reminds me of another Chinese myth of 'beauty snakes'. Those snakes infatuate innocent men by looking at them with stunning beauty and call their names. If they respond, the snake will eat their brains during the night.