Let me clear things up....
When a resin floor needs to be porous outside it is usually laid onto a porous sub-floor, such as a tarmac. There would be no point in having a porous topping when there is nowhere for the water to go.
Secondly, I don't agree with installing a porous floor outside. The resin would not cope with the rainwater coming through it. My best option would be to lay the floor as it's meant to be laid (a dry mix) then seal the holes and allow the rainwater to go to a drain. There are reasons why sometimes a porous resin is specified but won't go into it just now.
Another point is that eventualy dirt will build up in the holes and block the water from going through. Bad idea in my view.
Back to Billeboy's question.
Dependant on how much traffic is going to be using the resin.
Polyaspatic is relatively new compared to epoxy and PU but in my tests I have been left impressed with it. I suggest a PA primer then base coat, blind scatter with aggregate (maximum size 1.5 mm) then two clear coats PA seal. I used this on a temporary walkway to the main entrance of a major shopping mall in Glasgow, worked really well. Looks good, is taking the punishment of a lot of shoppers and is keeps clean - a positive aspect of this resin. Polyaspartic is a thin bed resin and fast curing, a plus in our climate.
For 4-6 mm aggregate you would need to use either epoxy or PU. The manufacturers you go to will put forward their most suitable product. If using epoxy we always apply a water based UVR seal over the epoxy (after filling the voids between the aggregate). This stops the blooming that will happen when water comes into contact with the epoxy within the first 5 days after installation. It also provides a UV barrier to protect the epoxy colouration.
I would never buy resins from a store. Don't know the situation in North America but here only the very basic resins are available in DIY stores.