r5 knull, r5 colossus or r2 sunspot

Gr8TonyStark

5star Colossus is sig 100 and 6star sunspot and 5star knull are unduped. Which champion shall i take up. Do these Champs find usage in 7.3 and 7.4.
Here's my roster and I am currently in 7.3.
Thanks.

ZAHIDMALIK1588

R6 Doom