Singed and Gangplank-- who to pick

Singed is wonderful. He can distract whole teams while you take objectives... but unless you're in a 5-man voice call or you're high Platinum+, your team more than likely won't capitalize on your efforts. Plus he's in major need of a rework.

For a waveclear champion that's just as quick at killing minions, has more damage overall, and has map-wide ability to assist, pick Gangplank.

Unlike Singed, he doesn't require a fully coordinated team to be successful. You can split on your own and R on top of teamfights, or join the fights and destroy tanks with your barrels.

That's if you want a waveclear champion. If you want a champion that can just distract the whole enemy team with tank stats, pick Mundo or Illaoi. Mundo can use his W just like Singed's Q, and Illaoi can heal so well in a 1v3 that she takes just as long to kill. And both are more effective at taking turrets or in teamfights.