I feel my Killer Wail execution is abysmal. I don't think I can ever positively contribute to a match when I use them, I dont know, so that's my least fav special. I want to get better with it because there are weapons I'd like to use more which have Killer Wail, like 52 Gal.
I felt pretty proficient with Ink Mines because I used Aero RG so much in my beginner days. I know all the most useful places to put them on nearly every stage. I agree they may be least viable, but from my own experience, I can use them more effectively than Disruptors, or maybe Point Sensors.
In defense of the undisputed loser of subs, here are a few key locations for Ink Mines on various stages:
-Moray SZ: Go to enemy's lookout above zone, plant one near the orange box just north of you. You're a hell of a target there, and this usually surprises people as they rush in to pick you off. Moray also has many other places that are easy to reach and effective for Mines since it is built around narrow ramps. The main sniping perch everybody knows and loves is another good spot.
-Mackerel SZ: The end of the enemy's corridor closest to their Zone. Camping in the zone and keeping this area mined has worked effectively for me before.
-Piranha SZ: Just after the conveyor belt of north of Enemy's zone. Another place where squids like to rush in carelessly, especially with the pressure of the timer.
-Flounder SZ: The top of the ramp ascending to the enemy's zone. A small square where squids will often rush up the ramp or ascend the wall of the tower to reach the zone. If they are reckless, they'll get splatted.
-Mahi Mahi SZ: Bit of a hassle, but the semi-protected platform where snipers and Aerosprays live is great, or the platform which raises halfway through the map.
-Ancho-V SZ: Probably not a great one, but I have to share: I once got a triple KO by placing one on the common sniper perch on this stage. That probably almost never happens. But the spot is simple enough to reach.
-Saltspray SZ: The place where the two ramps to the zone merge.
-Blackbelly SZ: Top of the tower (duh), or ledge just before they drop down into their zone.
Many of these are probably quite obvious. But if you feel so inklined to use Ink Mines, they can be quite effective.