Those two would have dramatic differences in water retention. For your layout I would recommend lava rock bought at the local hardware store.
Holds water really well, isn't too heavy, and your system doesn't require smaller pieces. Unless you're in a particularly hot arid region, you'd likely only need to water them once or twice a day.

Thanks Grizzman,
The table is inside in the basement, so should not get hotter then 75-80 in the summer.

I have a flood and drain with both, why you ask? Best of both worlds. I use it for a nursery to get plants started to go into my nft system. On bottom of the tote is coco choir, on top is a 1 ish inch thick layer of pea gravel. I sit the seedlings in rock wool 98 at a time on top of the pea gravel. Flood 2x daily 6a 6p when the roots start into the pea gravel they are easy to pull out. The choir stays wet and keeps the pea gravel damp longer. Once I have a half inch of root out we pull the rockwool starts then they go right into the nft cups and into the rails.

Initially I tried choir only but the roots grew into it and couldn't be separated because the roots were damaged. The pea gravel alone seemed to dry quickly. I like it this way. We are making one 3x bigger to take care of our larger capacity this year.

@ Rio_Grande
Hey thanks for the input! Sounds like you have it pretty much figured out! I like the idea of having both. The gravel would help to keep the algae off of the peat. The gravel if / when it does get algae on it can be re-cleaned and sterilized.

Glen

Thanks, but I will never have it figured out! Lol it's too much fun playing!