I play Mellka a lot and have struggled between those two. At first, I always took the one shot. Then, when I tried the pool, and now, I always use the tracing bouncy shots.
I like the one shot a lot, I’m pretty sure it does more damage than all 3 combined, making this the perfect choice if you simply want damage. It is, however, hard to land and requires a good ~2-3 seconds to start up. As if it only shoots the 3rd shot. I missed with it a lot, and generally felt like 3 was better because I always land at least 1/3. Rarely do I get all 3.
The pool is nice, I guess. It feels strange to pick an option that promotes missing, but hey, it’s good to cover all your bases. The problem I have with it is when you miss, you are typically WAY off. I mean, unless you are above them, a miss normally lands way behind them and I noticed my pools doing nothing. At most, they are preventing the enemy from standing there. I have the issue, now, of whether to aim at the ground where I want the pool to be, or to aim for targets. Also, keep in mind, you have to hit the ground, if you miss and hit the wall you will get no effect.
Now, the Blade Storm that allows them to bounce and track targets removes their explosion. I’m not sure what the explosion does, I’ve never seen it deal AOE damage and I’ve never seen it spread AOE venom. But, it definitely bounces off the environment, and oh my god does it bounce! This thing ricochets like a bullet, it is crazy. The velocity of the blade makes it hard to track effectively, and I have no idea what happens after they bounce off (because they are so fast), but I once, on Overgrowth, was aiming from the center towards the side of the “garage” near the sentry. It hit the wall going straight at it from the center lane and it bounced up and, like a jet, made this HUGE 90 degree turn towards the sentry’s direction. No idea if it hit its target, no idea who it was going for, but jesus… it looked like a jet flying around.
I prefer it for the bouncing more than the tracing effect. You can aim low and when you fire at targets it’ll bounce off the ground and fly into them. All 3 of these options are really poor. None of them make a huge difference, except the single shot. Mellka’s ultimate is pretty unimpressive, but she makes up for it by having amazing skills. Each of the three are just as useful, just make sure you pick the one that brings YOU the most use, because each of the 3 work in their own way and none are really all that great.