Probably the Old Republic, they where more unified then the New Republic.
__________________ "Vader's pulse and breathing were machine-regulated, so they could not quicken; but something in his chest became more electric around his meetings with the Emperor; he could not say how. A feeling of fullness, of power, of dark and demon mastery -- of secret lusts, unrestrained passion, wild submission -- all these things were in Vader's heart as he neared his Emperor. These things and more."
__________________ "Happiness is a lie. Life is horror. The light is always dying all across the universe. The last star will flicker out someday, when it does, all that remains is shadow. And I will be its king!"'-Amahl Farouk
The old republic enjoyed peace for 300 years where the NR constantly suffered from devastating conflicts.
The Old Republic at that point seems to be pretty powerful. Unless there are major technological differences, I wouldn't be surprised to see them survive the Vong better than the NR.
The Vong would be too big for the Republic of the Great Hyperspace War era, and would crush that comparatively small Republic.
The KotoR Republic, would likewise lose without much question, though in a better fight.
TOR era, that could be a fairly good battle. It's smaller than the Republic that the Vong faced, but does have plenty of Jedi and a strong military. I'd think it'd be quite possible to lose, and the Vong will certainly go very far, but the Republic may be able to make them hit their logistics limit again (unlike Sith, Vong can't really recruit locally to bolster themselves, save with their lowest-end forces, the actual warrior caste has a limited amount) and then slowly push them back. It would be a very painful experience, however. Vong ships are stronger than theirs are, and they have nothing that'd be too good against the Vong's combat capable worldship (it took a suicide SSD bomb to take it out by the NR).
I could easily see them getting 75~% of the Republic at max extension. And if there's major bad moves made, defeat is possible.
Registered: Oct 2014
Location: France/Rezée (near Nantes)
They r at war.... the war economy iz up. They have thoze artirfact like the ztar forge they have more Jedi...
Not any w-165 turbo lazer.. But they ztart to build deadly weaponz....
When the Star Forge was around, it was a period where the Republic had already received recent blows, and doesn't have much strategic depth of territory. Plus it's ships aren't particularly strong, and still need crews.