I think Apocalypse only stands a chance against Base Sentry given feats, but the caveat would be that since Apocalypse is more schemer than hands on combatant there isn't a big enough resume of battle feats or precedent to base the battle on. All we know is Apocalypse is somewhere around High Evolutionary level. I don't think on average that would be enough for a majority against some of Sentry's high end showings (Siege, current Death Horseman), but it would probably be a 5/10 or 6/10 Sentry split if it's the Sentry persona alone prior to Siege, with Death Sentry and Siege Sentry taking a majority.
Man, that... Given feats a regular Sentry is MUCH more powerful than the Void :-7 Let me make a list for you and anyone else:
(And of course we are talking here about the character being at his best and not being handicapped for the sake of the plot, something that rarely happened to the Void - so at best, the Void is more consistent than the Sentry)
(For references check out the revamped Sentry respect thread)
What did the Sentry do?
- Well at first, he defeated the Void in fights multiple times,
- Collective and he destroyed a moon during their fight in space,
- During his fight with Photon he destroyed planets, while holding back,
- in a weakened state he stalemated World War Hulk and even had the upper hand,
- he easily defeated Terrax,
- he easily overloaded the Absorbing Man,
- he oneshotted Attuma,
- he erased the memories from everyone on the Earth including people with heavy resistances like Omega Level mutants, Hulk, Thor and Doctor Doom,
- he fought through Dr. Strange's magic and oneshotted him,
- he overpowered the Molecule Man with his own weapons,
- he broke through Doctor Doom's force fields multiple times,
- he created gigantic craters with mere punches...
What did the Void do?
- he uses his infi-tendrils, which make him capable of shutting enemies down immediately (that is a big advantage over the Sentry indeed),
- he broke the Hulk physically (but he had an amp at that time, because he absorbed antimatter in the Negative Zone),
- he busted a bunch of Marvel Earth Superhero teams (three times, but to be fair there were not that many heavy hitters),
- he ripped Ares and Loki apart,
- he negated Xavier's and Emma Frost's telepathy and attacked Emma Frost back,
- he oneshotted a Doombot (funnily enough one of these defeated the Silver Surfer)...
And that's basically it ...
Judging by the scale of it all the Sentry has a better track record than the Void and he also operated on a bigger scale in my opinion. Especially the fact that he straight up defeated the Void makes it as clear as day for me.
Of course the Sentry unfortunately also has a bigger jobbing record, but oh well ... Brian Michael Bendis.
On topic:
There is basically NOTHING I know about Apocalypse so I'll have to pass on this one.
Based on resume Thanos is clearly above Apocalypse. However, part of that resume disparity is because of the goals each attempts to achieve. Apocalypse doesn't want to dominate the universe. His goal is to lead humanity/mutantkind to it's evolutionary apex, and as such a vast majority of his efforts take place on Earth and involve mutants only. That's not to say his abilities only work in that realm of infuence, it's just the place where he operates, and so there isn't a big enough scale for comparison. From what has been shown we know Apocalypse is somewhere around or above High Evolutionary level, but below full powered Onslaught level. I don't think that would be enough to beat Thanos unless the fight were purely physical (which is where Apocalypse might have an advantage).