Downstreamers. Their dakka is powerful enough to destroy Transduction Barrier and destroy Gallifrey itself. The Capital is a weak point here because it can be destroyed. Also Downstreamers are more "durable" and they have wider influence.
Time Lords have all different kind of hax and many temporal weaponries.
Pre-FVC DS can tank multiversal collapse, so are Time Lords with Ultimate Sanction. TLs would become beings of pure consciousness unbounded by time, cause and effect. From there, It'd be toss up in the air. Pre-FVC DS don't really have firepower to overwhelm TLs, but TLs can't simply overwhelm Pre-FVC's Regen/Durability
Of course, Pre-FVC DS too have their own 'Ultimate Sanction'. In which if they use it the fight will be Post-FVC DS against TLs all over again.
Apparently the Downstreamers survived the recreation of the multiverse, and actually transformed it from a finite multiverse with a limited number of universes, to an infinite multiverse with an unlimited number of universes. In this infinite multiverse, every possible universe that could exist does. Seeing that those universes where extraterrestrial life existed usually ended up with humans being killed early or never evolving due to alien interference, the Downstreamers isolated a sheaf of universes (a sub multiverse) where humans were the only intelligent lifeforms in the universe. They then built the Red Moon, a moon with a powerful "World Engine" inside of it that would wander this multiversal sheaf, teleporting from universe to universe, each time appearing in orbit around that universe's Earth (displacing that earth's original moon if it had one).
It would then open a portal that would teleport various hominids between earth and the Red Moon, and return again millions of years later to teleport them back. That is why different species of hominids evolved on different planets in the multiversal sheaf (this was done to help human evolution).
The Downstreamers were only omniscient in the original, finite multiverse. Once they expanded it into an infinite multiverse and created other infinite multiverses, they still had their original amount of power and knowledge (or perhaps even more), but it wasn't enough to predict everything in infinite universes.
Relatively early in the Downstreamers' history, they had built many gravity mines around supermassive black holes, the first one being around the black hole that formed the remains of the Milky Way galaxy. Each of these structures was galaxy - sized or so. At this point, it was stated that the universe had expanded to 10 quadrillion times its current size. Even at this point, the Downstreamers had shed their physical bodies and lived as energy beings, with a group consciousness (but individuals could form periodically and then rejoin the main group).
Even farther in the future, they were herding together all of the last remaining supercluster-sized black holes in the universe with a massive structure that spanned the entire universe (I mentioned this in an earlier post). The universe was much larger then, since it had been a much longer time since the last part of the story. So this thing was absolutely ginormous - maybe a low - end estimate would be 100,000,000,000,000,000,000,000,000,000,000 light - years across (based on the size of the black holes and the previous information, as well as cosmic inflation).
Well, there are already infinite number of universes in Manifoldverse even before FVC.
[“There are infinite number of possible universes in the manifold,” Anna said. “Of these only a subset – nervertheless infinite itself – are capable of supporting self-aware substructures. And those universes are characterized by a flow of time,…”] A quote from Manifold: Time before their ‘multiversal restructuring event’.
Don't the Pre-FCV Downstreamers rely on 3-D phemomena (namely black holes) to power their civilization and are crippled without the energy from such things? Could not the Time Lords rewrite multiversal laws of physics to their own advantage in that case? I don't know much about the Downstreamers, so I apologize if my point is incorrect.