Took some time to trim down, so first I'll say I love any and all of the Beast Boys and his Dolphin form is certainly no exception. Echolocation is a nice touch.
Arkillo is an excellent foil to Kilowog and his card really brings all that out with a shine. I'm not sure I'd run Yellows without him. (Also shoutout to Indigo-1 and Saint Walker)
Lastly Aquaman (II) is epic, this is the Aquaman you can envision up there fighting with the gods and monsters! Definitely reflects the hardcore Aquaman I know from Injustice.
My two picks are also the two I feel are the most inventive.
Blue Beetle (Jaime Reyes) - I love his character and the card really lets you feel like you're making the decisions in what he can do and how he reacts.
Ocean Master - I always thought it'd be cool to run a water army and this is the way to do that, I haven't played him yet, but I can only imagine how fun it is flooding the map.