I was wanting to do hydrotron or the coconut. I was not wanting to do the hydrotron in the whole tray though, just in the pots. I have heard that coco stuff works good.
I picked both mediums because I read it is very difficult to overwater coco or hydroton. I had read quite a few good reviews on the coco, and as I wasn't going to fill the tray with plants, I put the hydroton in between the pots. I did this for two reasons. First, it takes up empty space in the flood tray to allow quicker floods with less total reservoir requirements. Second, I knew that if the roots grew outside the containers onto the tray, the light would kill them. Being my first grow, I didn't really know how big of a container I would need for good root develoment, so I figured I'd hedge my bet. The only downside to my system in non-portability of the pots.
Good luck with your decision.