I suspect pulling is better than pushing, but it's probably a small difference -- assuming air flow over required surfaces is adequate in either case (ducting applied to heatsinks, etc.).
The difference to me is this: dust deposition is greatest where the velocity and shear are greatest. This occurs at the fan itself, immediately downwind of it, and to a diminishing extent at a distance.
If you can have laminar flow, expect very little if any dust deposition at all.
A wide intake, that's not being stirred up by fan blades, may not provide laminar flow, but it can be low turbulence at least. It won't be high velocity, so don't expect stupendous power density.
That's only about dust, of course, which drives long term reliability, again as long as temperatures remain adequate.
It may well be a higher priority, over the specified lifetime of a product, that smaller size or lower cost is the bigger target, and for that, the direct, downstream airflow from a higher speed fan is required. Probably this dominates in most consumer equipment: laptops, PSUs, graphics cards and such.
So I think it divides into two overlapping regimes, where for short lifetime, dust really doesn't matter and the intense flow is desired, versus longer and longer lifetimes where gentler flow is required, and also better quality fans (probably brushless ball bearing?); and screens, filters and sound dampening are also desirable.
Two handy examples: my TDS460 oscilloscope has a huge fan in its side, 5 or 6 inch dia. Not very fast, so on the side of lower flow. It is "sucking" mode. It draws air over stacks of boards, not really ducted to heatsinks or anything (that I recall at least). It accumulates very little dust, surprisingly little I would even say.
Other example: my 21" Trinitron monitor. This is an extreme example because, obvious gimme, it doesn't have a fan at all, it's convection only. It is tall enough to develop a modest flow, though, and there are perforations at the bottom and top to draw in, and let out, the air. It collects essentially no dust -- even more remarkably, this includes the high voltage connections! And this despite being almost old enough to drink (if it were human), and yes having been in service much of that time, not storage!
Tim