It depends on whether you are eco or frontliner/suicide, so I'll divide them up by that...I generally think of early game as very brief, with mid-game being the period before
Frontliner/Suicide:
Early game:
TEC...they get all 4 early units (LFs, LRFs, flak, and corvettes) with only 2 labs, and have no particular weakspot in their early military...Corsev with dem team/salvage, Marza with raze planet, and Sova with missile batteries/embargo are very strong leads and give TEC lots of early game options...have best repair platform, and are only faction that can get early repair cruisers....
Advent...they have the best LF, flak, and corvette, with the illuminator being their only early game weakness military wise...Progenitor with malice or Discordia with fracture are very strong leads and are brutal against frigate-heavy fleets...having culture at tier 2 is particularly useful since frontliners don't often have the funds to make a decent trade network...
Vasari...LF and flak are weak, LRF heavily depends on weapon upgrades to be useful, corvette is tier 2 which is huge killer for expansion...Jarrasul with nanites or Vulkoras with siege platforms are good starts depending on the situation, but overall TEC and Advent have better caps for early game...weak repair platform, and no early access to any economic structures...neutrals and Orky are only real advantages Vasari have here, other factions have much better fleet...
Early-Mid game (before titans):
Advent...now have illuminators no problem, so arguably best fleet...mid-level caps support fleet extremely well, lots of damage output here...destras and aeria's are strongest of their class before late game weapon upgrades, more viable for Advent than other factions...trade and culture are both viable even to frontliner...
TEC...still have good fleet, but no longer lab advantage over Advent or Vasari prototypes...mid-level caps do not support fleet as well as Advent, Corsev is really the only powerful AoE at this stage...trade and culture are both viable even to frontliner...
Vasari...fleet still on weak side, though weapon upgrades are leveling the playing field...don't have AoE cap abilities that Advent or TEC do...culture viable but trade not so much for frontliner....Orky is only redeeming factor here...
Mid-game (first titans):
TR...Ragnarov with snipe/scattershot is best low level titan, excellent at dealing with both frigate swarms and sniping caps/other titans...
AR...Eradica good against frigate swarm, combos well with excellent fleet and excellent AoEs from cap abilities...repulsion is viable now, gives Advent options...
AL...don't have strong early titan, but still strong fleet and cap AoEs...
TL...weak early game titan, but fairly durable...
VR....good titan against frigates, but fleet is weak in general, no good cap AoEs...still hurting from later trade (if at all)...Orkies still good advantage
VL...weak early titan when frontliner, same weak fleet as VR, no good cap AoEs...still hurting from later trade, Orky only good advantage now...
Late game:
AR...wail is extremely useful defensive measure...Eradica with Discordia or Progenitor is powerful combo...excellent fleet, only weakness is focus fire ability of LRF...guardian+repulse makes for very powerful titan and bomber spam
VR...jumping Orky makes for excellent offense, titan excellent against frigates...fleet better than TEC now, have PM upgrades and have incorporated best bomber...
VL...strip is good, but only helps if making ground...strip not around long enough to really make lots of headway fleet wise though, likely no kostura or developed phase network...titan is weak without the kostura+strip strategy viable to eco player...fleet still behind Advent, but addition of bombers and more developed weapon upgrades puts Vasari fleet above TEC...
TR...Excellent titan, good against both single targets and fleets...fleet is now weak with incorporation of SC as TEC have weakest fighter and bomber...RB gives good options...
AL...extremely powerful fleet, but no options like RB or wail, and titan depends heavily on fleet...
TL...double SB is more annoyance than powerful advantage, relies heavily on RB...titan is weak...weakest fleet over all....
Very late game:
VR...excellent titan and jumping orkies...superb bomber and fighters, excellent PMs...
VL...SttC gives team better overall position, frontliner now more in position to make full use of mobility...not as powerful on offense as VR, but SttC allows attrition strategy
AR...wail and Eradica give both good offensive and defensive options...extremely strong fleet....
AL...extremely strong fleet, very difficult to kill...
TR...titan very good, but TEC have weakest fleet...RB is only redeeming quality...
TL...weak titan, weak fleet, double RB is only redeeming quality...
Eco:
Early game:
TEC...akkan has excellent colonize ability, tier 2 trade excellent for early feed...tier 1 corvettes make them viable for early expansion
Advent...tier 1 corvettes make them viable for early expansion....culture at tier 2, trade at tier 3, not as good as TEC but better than Vasari
Vasari...tier 2 corvettes make them less viable for early expansion...both culture and trade come later...neutrals is only redeeming factor
Early-Mid game (before titans):
TR...TAR allows rapid expansion, easily fastest growing economy...in good position to get first titan...
TL...lack TAR that TR have, but otherwise same advantages...
Advent...don't have as good population techs as TEC, no trade techs..
Vasari...last to get both trade and culture, neutrals is only economic advantage...
Mid-game (first titans):
TR...TAR allows colonization of central planets, explosive economy....excellent titan for throwing at frontline...
VL...SttC now online, massive influx of resources poise VL to get titan and kostura very early....
VR...jumping orkies good for assisting allies...
AR...Eradica good titan to assist frontliners...wail is option for defense if frontliner falls
TL...good trade techs, but no other redeeming qualities...
AL...no redeeming qualities at this stage
Late game:
VR...jumping orkies assisting on multiple fronts combined with full mobility via phase network allow eco player to assist almost anywhere quickly and effectively
VL...kostura+SttC brutally effective, titan excellent for mobility
TR...excellent titan, RB for pinch defense, novas excellent for weakening enemy
TL...RB for pinch defense, novas excellent for weakening enemy
AR...wail for pinch defense, excellent titan
AL...no redeeming qualities since unlikely to have high-level titan and caps
Very late game:
VL...SttC plus best mobility allow VL to surive while outnumbered...attrition strategy can lead to inevitable victory...
VR...jumping orkies plus excellent titan and excellent mobility make for quick and powerful offenses and defenses...
TR...excellent titan, novas perform excellent attrition, RB for good defense...
AR...wail for good defense, vulnerable to novas...excellent titan...weak superweapon
TL...novas perform excellent attrition, double RB good for defense...
AL...likely lack XP to make extremely strong AL fleet...weak superweapon...
If only you could achieve this level of godness with every post--then again that wud be asking too much of you.