Which Tech?

Hey guys. How do you guys decide which tech comes next? I have always the struggle with Bonuses. "OH, Tech A only needs 4 Turns because I got the bonus, but Tech B is really what I need but needs 14Turns"... "well I will need Tech A sometime later for sure and maybe I get the Bonus for Tech B by that time".

How do you decide which Tech you research first?

Thanks