Great White Shark (Thundoria Harbor) is the one with the highest attack, but its defensive stats are pretty bad. It's great for a seavoy for farming, since speeds the process up by quite a bit.
Eagle (Icicle) is the one with the highest health and defense, but likewise its attack isn't great. It's pretty useful for Seavoy battles though, since you will need to be quite tanky to survive the opposing sea fleet and deal as much damage as you can with your voy. Moreover, due to how tanky this ship is, it's great for a maze character as your chances of surviving any potential sea threat increase greatly in comparison to other ships.
Lastly, there's a weaker ship called Goddess in Shaitan. It's basicly a weaker version of Eagle, but the fact that you can build it in Shaitan is awesome, since you have to sail all the way to Shaitan with other boats. But the reason why it's great is because it provides a solid (Decent attack, decent defensive stats, decent speed) ship for anything you might want to do around Shaitan. Whether it's for farming purposes, salvaging in treasure gulf, Story quest or a quick ship for yourself, your seavoy, your buffer or whatever for mazes. Granted its stats are subpar, it's an overall multi-purpose ship if you don't want to move your main ship from another dock (Especially if far away).