Thanks for bringing this topic up. I spoke to some people, did some research, but was none the wiser after a few weeks
I recently had to install decking for my planter. Some people recommended composite (benefit is more lasting, but a little more expensive than good natural timber), some people say there are 2 grades of Chengal (and every contractor you speak to insists that he is using the best grade), some people say go for recycled plastic lumber, etc.
In the end, I used my tenant's agent's trusted contractor for "good" Chengal. Can't remember the dimensions, but paid $1850 (quote for the recycled plastic lumber was $1700; can't remember for composite). Photos are attached. Still too soon to see if it warps, fades, etc.
As an aside, some deckings can be installed such that you can lift up several of the timber planks at a time, so you can (theoretically) use the empty space underneath the planks as storage.