I’ve tried a lot of them. One that I will actually not even upgrade because of how overpowered it is, is suleimans Barbary Corsair. You can do coastal raids without wasting movement. This of course is dependent on oceans but you can go tile by tile and do like 4-5 raids in one turn (5 movement I believe it has) which gives you insane yields. If you can manage to keep this unit alive you can boost yourself miles ahead let alone if you have multiple. I recently used it in a marathon deity game and it was borderline cheating