When I ask, what is the most valuable investment? It is hard to argue that Tech Level is hands down the most valuable. However, because of cost restrictions, economic and war strategies, other Tech has value.
The question of what to invest in the first column, Since Tech is not available, it seems to me that Warp, Energy and Jumpgate are the obvious go to Investments. Although, an early investemnt in an outpost can pay big too, but because it costs 3 Research Tokens, is often skipped for a first or second turn purchase that is cheaper.

WARP ****
When you see your enemy buy Warp, you are instantly jealous! It is such an advantage to be able to move faster then your opponents. It gains you first strike, more opportunity to race to locations, whether planets, Unknown Technology (If you are playing with that Optional Rule) or your enemy. Good movement is powerful.
Face it though, the Warp adds you want to buy are in columns that gain you more then +1. However, Each round, it is so important to plan and remember what your going to invest in and what others invest in often influences what you need to survive.

Energy****
it is so easy to think you have enough Energy. But you are probably wrong! Plus, every Energy you invest in the Technology Investment Table is equal to gaining a size on one of your Planets!
That being said, Energy rules when you want to gain Initiative. Energy is also the lifeblood of some Races (If you are playing with that Optional Rule) and greatly needed to keep your squads traveling through space energized.
Yes, the fourth column Energy Investment is the best, unfortunately, strategy often forces our hand to make other purchases. Still, that is equal to three additional building centers! One is good, three is huge. Of course that first column Energy purchase at the cheap cost of 2 Research Tokens, pretty tempting...

Jumpgate****
At a cost of 1 Research Token, this Investment can be purchased on your very first Investment Phase! Of course it is totally useless, even detrimental if that planet is lost to the enemy! However, setting yourself up to be ready to connect two planets through Jumpgates gives your squads great mobility and even if you don't buy your own second Jumpgate, having one will automatically connect to an enemy planet with a Jumpgate that is captured. Which can make holding a recently captured planet much easier.