What can the aem stage 2 engine management do that the Hondata s300 cant

 

That's a loaded question. Quite a lot, technically speaking.
Practically speaking, there are some noticeable benefits but if you don't already know and you're tuning it yourself, I'd suggest Neptune rather than either of those. Certainly not an AEM EMS for a noob.
If someone else is tuning it, use whatever they can tune the best.

 

Ok thanks for the input

 

I went from chrome to hondata to aem v2 (what I'm on now)

The aem is way more advanced from my perspective. Lots more you can do and the car runs a whole lot smother. The new update has a flex fuel option now. You can run e85 and 91 and not make any changes to the tune. You could run half 91 and half e85 and the ems blends the tunes together on its own. Just need to add a flex fuel sensor and tune both maps. English racing did a video on this look it up on youtube.

Disadvantage is the so called "tuners" who say they can tune aem really don't take advantage of what it can do for you. They just want their money as fast as possible and leave you with a wot tune and a half *** part throttle tune. (I'm not speaking on all tuners just the ones if came across)

What I did was download the manual and learned it all myself and started tuning my own car. If it blows its on me and no one else.