Pi3 runs Deberian very well. However the Zero is a bit pokey, I understand it is not as powerful but I don't want it choking out. Any comments on this OS? dietpi.com/
The RPi Zero has a single core 1GHz CPU, while the RPi 3B has a quad core 1.2 GHz CPU. The Zero is going to be inherently slower.
The question is going to be, what are you doing with it? The Zero isn't intended to be used as a desktop computer. If you are using it without a GUI to run typical programs on it's own, then the choice of distro won't really make much difference, unless as said previously, you are running into a RAM bottleneck.
I haven't tried DietPi, but it looks like it doesn't even come with a GUI, so there's not a lot to be gained there versus using Raspbian with the GUI disabled. However, what DietPi does seem to offer is easier configuration without a GUI.
I would suggest there's a trade-off. DietPi seems to be easier to configure for situations where you have an application you want to run in an "embedded" configuration. Raspbian seems to be better suited if you are running it as a desktop with monitor, keyboard, and mouse plugged in while you develop a program interactively or just fiddle around learning. There is also probably a lot more information about Raspbian on the Internet which you can google if you are looking for answers to particular problems.
So, I would suggest that it's a trade-off rather than a clearcut answer in favour of either.