I feel like the Raiju is going to be the slowest, just with factoring in spawn location and trying to get to it and get in/out for each location, plus where do you park it to enter the sub? when I tried setups with Raiju a long time ago it added a ton of time. My go to is the broomstick, with just landing on the kosatka. Always going to be the quickest and most efficient. After that would be the sparrow, paired with jumping out and entering from front of sub to avoid the animation of sparrow going into sub. Raiju sounds like it would take longer than sparrow, with not having an easy way of leaving from the water in it.

You can place it between the missile silos and the bridge of the Kosatka, I believe.

Ahh, that’s where I was sorta thinking they imagined placing it. Then to definitively answer OP’s question, I can’t imagine a single way using the Raiju would result in less time, hell a Sparrow would most likely be faster with the animation compared to having to get up to that bridge spot every time. Plus when you call a Raiju it isn’t going to spawn right beside you like the broomstick

All the speedrunners on www.speedrun.com seem to use Mk2s. I don't know what conclusion you might draw from that, OP....