Whether one is "better" than another really depends on your criteria!
Studio Fix (powder) is great for oily skin. Because it's a powder, it's very absorbent. It has great staying power and buildable coverage. It's very fast to apply (just brush it on with a big brush and you're good to go). Cons for me are that I sometimes find it a little too powdery even though my skin is extremely oily. I tend to use it as a finishing powder over, e.g. Studio Fix Fluid, when I want to be very matte and polished.
Studio Tech is a somewhat creamy foundation, if you have oily skin then you may find it gets oily quickly. It has a very nice soft finish to it, good coverage, which can be sheered out by spritzing Fix+ onto your brush. Cons: The staying power is not as good; if you have oily skin it probably won't wear as long as Studio Fix. Also you go through this stuff really fast!
I hope that helps... personally I have both, but then I like to switch my foundations depending on mood / occasion, so yeah! They're both good, it just depends what you're looking for really.