On a water I personally chose to have pets that assist in sealing because you can't really hf your attack-based pets. Unless of course you have your own team and a fire that can hf your waters pet.
I really love Shasha. Freezes 2 which increases damage dealt on the enemy. I scrolled my Shasha well from lvl 20 and now she is the only one in my team that seals. (I only have a team of 3 and my water is a killer). But since I scrolled Shasha nicely and am lvling her, we manage just fine.

You want a sealing pet? An attacking pet? A healing pet?(I love Angela... just sucks you can't burst her) In the end, all up to you :)