Who is stronger at full build, Olaf or Trundle?

They both serve different purposes.

Olaf is probably one of the best bruisers for diving an ADC, and succeeding, because of his ult. He has no hard CC or real utility, so he really has to pick his fights well. Hard engage comps accommodate his playstyle. Very offensive-oriented champion that rewards calculated aggressive gameplay.

Trundle is better at peeling, disruption, tank shredding, and provides more utility. However, he's probably one of the worst bruisers at killing squishies due to his lack of burst damage. He's better on poke comps and counters hard-engage. Rewards defensive-oriented, proactive gameplay. Punishes bad positioning hard with his Pillar.

saying full build is not alot of info

Trundle forsure lol.

trundle

In a 1v1? Trundle. Vs a team full of cc? Olaf.

Trundle, because a full build Trundle is probably one of the hardest characters to kill in the game and if even a single member of their team dies, he gets a huge heal. People don't realize it, but Trundle is, in a way, a lot like the Katarina when it comes to team fights. Even one death can make him snowball.

Depends on the build and what you mean by "stronger".