Since speed is equalized, the only thing The Runner has going for him is his Cosmic Energy Manipulation and Matter Manipulation. The Runner seems to be low on hax compared to other Marvel characters, which will put him at a disadvantage against Buu, who has much more hax than other average Dragon Ball characters.
With Buuhan, from the Cell calc putting Cell at ~1,000 Foe, we can say that through the SSJ Multipliers Buuhan can responably be at around over 10,000 Foe; while his bare minimum is 2,000 Foe, just in case people don't care for the SSJ Multipliers.
This puts Buuhan at over 10x The Runner's strength, and with speed equalized, Buu also has Magic, Absorption, Power Mimicry, Healing, Afterimages, Transmutation into candy, and Mid-High Regen.
Buu gets my vote, and even if this is supposed to be Fat Buu, we can still use the bare minumum I listed before as his strength resonably; and Fat Buu would still have all of these abilities.