Just to be clear, I put Black Hole ahead of Rakata simply because Black Hole doesn't have set bonuses. These make a noticable difference, at least for me, since the abilities that got the bonus for my Op healer were for my main heal, and the buffed crit really helped.
In any matter of opinion though, yeah I see them as basically the same.
The nice thing is you can put the BH mods/armoring/enhancements in Tionese/Columi/Rakata shells and keep the set bonus.
What makes one tier of gear better than the other is the "stat budget". Each tier has more points to allocate for the stat improvements.
However, each mod has three variants
. Unlettered, "A" variant and "B" variant. Both the "A" and "B" spend the stat budget on endurance, which is bad for dps and healers. So a Rakata Artful 25 mod is going to be better than a Black Hole Artful 25A mod.
If you can stick with gear that supplies unlettered mods, and has enhancements that hit the secondaries you're trying to improve, the gear progression works is as expected. However, to get the elusive "Best in Slot" it requires mixing and matching mods and enhancements out of different pieces of gear. Sites like AskMrRobot help figure out how to put your gear together.
Here are some links to Tionese (23), Columi (24), Rakata (25), Black Hole (26) and Dread Guard (27) Artful Mods (unlettered). You can see that each tier is better than the one before.
it's can get expensive, but you can keep your Tionese/Columi/Rakata shells, rip out the Black Hole armoring/mods/enhancements and put them in your shells to keep the set bonus.
Once you get Campaign/Dread Guard amoring, the set bonus is no longer tied to the shells and you can put them in any moddable gear.