Rod is correct. Composit deck boards - any brand, are not as stiff as wood when comparing the same size.
Honestly, I can't recall the name of the composit I used (Choice Deck maybe) - the gray colored stuff they sell at Depot. Nice looking stuff - wood grained and all. They recomended a minimum of 16" OC for the joists. Since the old deck was framed with 2X10's 24" OC I simply added new 2X10's between the old ones and ended up with 12" OC. Just stable enough. IMO, 16 OC would not be adequate - too much bounce between the joists.
Another consideration for you. Since the composits are not as stiff as wood the top plane of the joists needs to be very flat. If they arn't the resulting deck surface will be very wavy. You can get away with this a bit more with wood because each peice is different from the next which distracts the eye. Composits boards are identical. Also look into what fasteners you should use. Most composits are dense enought that driving nails into it will be quite a challenge. Some composits are so dense you may have to pre-drill. I pre-drilled and used SS screws with a very small finish head. The boards mushroomed a little when the head went in but a tap or two with a hammer flattens the mushrooms. Unless you really LOOK for the holes you can't see them. They do make some rather nice screws now that require no pre-drilling, leave no mushroom, and come in different colors.
Composits - due to the plastic in them, tend to get hotter than wood. Obviously, dark composits will get hotter than lighter colored ones. Depending on your deck's exposure you may want to consider this issue.
Some composit manufacturers - I think Trex is one, produce composit railing material if you wally want to match the railing to the deck surface. None of the composits, however, are rated as structual material so the produced railing my end up feeling a little whimpy. I used regular pressure treated pine for my railing, painted the majority of it but capped the top rail with the composit to visually tie the railing to the deck.
Finally, don't let anyone tell you they are maintenance free. They will stain from leaves, the color will lighten with exposure to the sun. They will grow a little mold. Like any deck surface, depending on it's exposure, you will have to clean it. I have to PW mine every season.
Happy to snap some pics if you'd like.
Dan