I like Port Mackerel in splat zones and turf war because it promotes defensive play and ink coverage more than any other map. The three narrow corridors in the center of the map make approaching the other side of the map more difficult than usual. There is no way to flank; every time you travel from one side of the map to the other, assuming the match is neutral, your presence will be known. Weapons with splash walls, high range, or sometimes even suction bombs have a significant advantage when pushing through or defending the corridors. This leads to some interesting battles in which the players constantly switch corridors or hide behind one of the crates in order to find an opening to the other side. These types of 1v1 battles are a lot of fun for me.
This map promotes ink coverage more than any other because of how linear the layout is. If 80% of the map is covered in your ink, you can easily detect the enemies' approaches and maintain a strong defense. Once your team reaches the other side of the map, blocking the two corridors at the enemies' base is simple, and in this scenario, the enemies will have to approach the middle of the map through their alleys (you should anticipate this) and/or charge up their specials by shooting over your ink. If a teammate dies while on defense, you can hide behind a crate and let them super jump back. On this map, comebacks are realisticly possible, but extremely difficult.
I like this map in tower control as well because there are so many opportunities to effectively use splash walls for the objective. They are probably overpowered, but it makes gameplay more interesting. I'm not a fan of this mode in rainmaker because of how simple the gameplay is, but I admit I haven't played it that much.
This is unrelated to why I like the map, but it's worth noting. You can sometimes use the kraken to get to the enemies' alleys and control at least one of them. It works especially well with the 96 gal deco and krak on roller with the quick respawn gimmick.
I don't like Kelp Dome because it's very open. There are too many entrances that your team has to watch and too many flanking routes. It's not a bad map though, it's just my preference.