From a technical point of view, they are pretty much the same, and pretty much different ...
They are the same because they both use the 3D harware basically the same way (the videocard is still the same).
And they are different because they use a different philosophy, OGL is an "automata" and DX is a "nodebag".
From a hardware point of view it depends of the videocard:
- 3DFX are Glide based but can run DX and OGL, although OGL Layer isn't complete on most drivers, while DX are.
- nVidia are OGL based but can run DX very well, except little problems (nVidia is SGI, SGI is OGL, and so on ...)
- for other manufactuerers i can't tell, because i never have any of their cards, i think most of them run best in DX beacause of MS but ... you'll have to find out by yourself.
From PSX Emulation point of view, it depends of the gpuPlugin.
The best way to know which is better is to ask the developper itself, don't you think ?
But remember, you hardware capabilities comes first
EDIT - I just realized i used DX instead of D3D. :innocent:
Sorry if it shocks anyone but they're so interleaved i'm confusing myself.