Okay, so here's what the powers of the era seem to be like as of 2350:
Terran Hegemony: Powerful, expansionist, fairly stable after McKenna's coup in 2314. Easily the top dog.
Lyran Commonwealth: Newly formed in a three-nation merger. Government still isn't terribly functional, and won't be for a while.
Free Worlds League: Best-established of the big five, fairly stable and well-run.
Capellan Commonality: Fairly small, has corruption problems, not well-regarded by its populace.
Sarna Supremacy: Not much info. Seems generally competent, if small.
Tikonov Grand Union: Falling apart, generally in horrible shape.
Chesterton Trade Federation: Almost no info available, may already be defunct.
Federated Suns: Not much info, seems generally competent.
United Hindu Collective: Small, big believers in armed neutrality.
Draconis Combine: Large, expansionist, currently tied up pacifying Rasalhague.
Principality of Rasalhague: Currently being turned into a puppet state by the Dracs - effectively a guerrilla force, not a nation.
Rim Worlds Republic: Politically shady, but fairly functional as a nation. Busy throwing off their pirate roots and building up educational infrastructure.
Taurian Concordat: Small, fairly effective for its size, not yet known to the universe at large.
(The Outworlds Alliance, Magistracy of Canopus, and Marian Hegemony don't yet exist. I don't know of any other obscure powers not listed here.)