it seems that advent are better, due to OP units, but their crappy eco and my lack of playtime make me dislake them, i dont have enough micro skill to fully use them with their full battle potential and so their eco don't allow me to compensate casualties with production as easely s with other races.
so actually i found vasari more powerful just because their eco being better than advent i can spend more time microing battles than my empire and with their ships necessiting the biggest amount of micro of the 3 races i have more results with vasari than advent
BUT , as i said my average playtime isn't really high so i favour TEC, their eco can compensate most of my micro lackness ( who said noob friendly race? ) and i thnik they are the weakest SO i favour them 
since starcraft i favour the "weakest" race in any startegy game i play, just because... they are weaker 
winning with the weakest means you are just better not you are using the winning stuff
( and sometimes that you are harder, mentally stronger and officially the most bad ass player to play against ===> don't know how to translate my own language here to illustrate what i think, " le plus fourbe" )
but to join the game background/ scenarii , TEC will win the 3 races struggle, in any case. Just because their core worlds are still untouched and start full warfare industry mobilization ( soz dont sure about this word)
What can do a one world start galactic empire like advent against thousand worlds like TEC dominion ? what can do billions of psy enhaced workers against billions of billions of workers ?
watch WW2, for every tank or plane germans produced (strongest or not) allies produced 10, you can be better one time or another you start running out of ammo or luck ...
and vasari you will say ? a fleeing race ? peoples with just their shoes, a bag and a gun ? peoples mostly relying on slave labour ?
slaves don't make great workers... a big pile of stones ( pyramid's
and yes i know it wasn't only slaves ) is one thing a nano-technology madnes like a starship ? wow would you really put your life in the hands of an angry bunch of surrended ennemies ? O___O
no really TEC just should have win. But as some peoles said the biggest change will be the 4th race, vasari nemesis ...
we gonna see 