From strongest to weakest, top to bottom.
Asuryani -High Tank,(63 armour with holofield???) Insane sustain damage, Insane Burst damage, High speed. Expensive ships.
Chaos- Because of Slaughter builds (240 speed 1600 hp , 63 armour huge close range dps, even better with AP rounds) Cost efficent carriers, otherwise pretty underwhelming. Chaos god favours.
Orks- Cost efficiency per HP/armour , fighter bombers, Traktor beam. Slow. Has faction specific skills.
Drukhari- High burst, fast, invisible, pretty squishy but overall very good.
Adeptus Astartes- Can be good or bad, but certain builds make them hard.
Tau Protector - Big damage lots of fighters, nice torps. Weak to ramming and torpedos.
Corsair- Hard counters certain factions, but gets stomped by others. Flimsy. High skill cap, so can be insane good.
Necrons- High tank, regen hull, mass recall to silent running LC flag. Pretty straight forward. I'd say a low skill cap, but positioning, and map control and placement decisions make up for slow movement.
Imperial Navy- All around good. Struggles against eldars unless LC spam.
Adeptus Mechanicus - Just IN cruiser variants with Nova cannons attached. Same thing. But with poor troops.
Tyranids - Bit slow, but some battle cruiser builds are good and competitive.
Tau Merchant - Tanky, but still suffers from moral hits of protector and does not get their damage also poor troops for tanky slow faction.