One notable thing that's made me choose Sludge Wave over Sludge Bomb that hasn't really been mentioned here is that it hits everything. This is partly incredibly useful for heard encounters in gameplay, but I personally also find it useful for group battles as it hits both my opponents at once. Yes, it does also hit my other pokemon, but for me this is worth it as both my main pokemon are poison type so it won't be very effective against them and can't poison them. I know this is quite a specific reason that I chose it, but I thought it was worth mentioning.