1st Age
2nd Age
3rd Age
4th Age
5th Age
1st - Thanos beats him with out much effort, mostly due to the power consumption effecting Spawn. Even recovering takes up energy.
2 nd - Thanos losses. At the vary end, he accepted his role as King of Hell. And can vary well wreck havoc across dimension. That and Thanos has no real answer to Time manipulation.
3rd - Every bit as powerful as 3rd Age, unless Thanos can remove his suit, or forcibly revert him to human form. This version could give him trouble, since the power limiter is effectively removed. He is no longer penalized for power consumption. Not only that but this version can summon forth his Legion of 4,000 plus Legion of Spawn.
Ultimately Spawn would lose, since he can not muster enough power to relatively do any damage. And the swarms of Spawn’s would be taken down by the masses. But again, thanks to that insane regen, powerset, and no limiter to energy consumption. It would be a long fight.
4th - Spawn destroys Thanos. He is on par with Urizen, God, and Satan. Thanos can do absolutely nothing to this Spawn.
5th Thanos destroys this version of Spawn. The weakest version, seemingly relaying mostly on the suits abilities.