That question is invalid. Is the same as asking "what is the most powerful champion in league of legends?" there is no fixed answer to those questions.
Even if we try to narrow down a few chmpaions that are super strong with scripts( like, Kyle for Top, Kindred for JG, Yasuo/Yone mid, Kog'mawa for ADC, Senna/Lulu for SUP), they still can be very weak if not played right (like, dying a lot as Kyle before level 6 and not farming propely, or dyring a lot as kindred trying to get marks, feeding as Yasuo/Yone because you don't know how to ward or your champion power spike, as Kog'maw trying to win the lane instead of focusing on farming and scaling, as SUP not knowing how to ward, put pressure on enemy adc and playing well with your ADC).
You got figure out your playstyle (agressive/passive, late/early game), then choose a champion that works on the role you play and that matchs your playstyle(don't pick veigar if you are trying to win lane or Lee Sin if you plan on power farming for example) and get yourself used to that champion script, know what it will do and how it will do it, twek its configs to fit your well and then naturally that champion that you choose will be hella strong. Repeat the process with a few others champions and you would have a decent pool of champions to play with a very well configured script.