Moji first. Evolve him to his secret OP robot demon version, Mechamoji.
Z19 GaryOak
I think first picks would be Esapidon, Mechadino/Coldheart and Djinzam. A lot of mons actually gain quite little by ultra evolving, so typically you prioritize the ones that make the biggest leap. SE twinkillers in particular make a giant leap by gaining Timestrike. For epics, go with Ninjagust/Frostknight and Beetlebrave. All almost useless second form but incredible utility fully evolved.
Do not listen to gary
But if you want to ultra evolve a legend, do terrordragob
Owait
Do ezapizeron and or the new free legend
I don’t know why you don’t believe in the Mojinator. This will be your downfall
Z19 GaryOak