1) Marquis of Death - could exact universal change with the snap of his fingers
2) Legion - Capable of creating global scale reality warps/pocket universes at the drop of a hat - full potential yet to be revealed
3) Franklin Richards - again capable of creating pocket universes and said to be on par with a Celestial at full potential
4) Mad Jim Jaspers - somewhat overrated on this forum when you actually breakdown his demonstrated feat but still very powerful. 616 Jaspers feat was actually creating a global scale reality warp as stated on panel. However based on observations of his alternate reality counterparts his reality warps sphere of influence was hypothesised to have the potential to spread over time to encompass the universe and potentially be a threat to the greater multiverse if left unchecked. So whereas others higher up on the list demonstrated the ability to exact global or universal scale change in the blink of an eye, Jaspers had to gradually build up his sphere of influence. So he only ever warped reality on large portions of the Earth before he was stopped. Great potential though
5) Jamie Braddock - Again a global scale reality warper as far as we've seen to date. Good showings in terms of strengthening Psylockes defences against First Fallen and in Excalibur against Rachel.
Other contenders:
Matthew Malloy- Massive energy manipulation, psionic and reality warping abilities. However we didnt get to see enough of him on panel unfortunately to rank him.
Jean Grey - Its stated on panel that what makes Jean Grey special as opposed to the other hosts the Phoenix has possessed is that it is actually her mutant ability to tap into the Phoenix Force. With that in mind she'd be number 1 😱 but im too time restricted and old these days to argue the point 😉