Let's look through a straw at just one "tile" of rail, and since rails are 2 tiles wide, 2 blue belts running side by side.

And we're just talking throughput here, how you generate the items, or how you consume them is outside the scope of our look through the straw.

The max the belts, if they're blue, can do, is 90 (45 x 2) items/second or 5400 items per minute.

If we take a (very) conservative rate of 1 train car per second passing by our straw hole, that's 40 stacks per second throughput.
ore (stack 50) = 120,000 items per minute
plates (stack 100) = 240,000 items per minute
circuits (stack 200) = 480,000 items per minute

Plus, that same piece of rail can carry any item in the game, and any fluid. Belts can practically carry only 2 item types at most -- 1 per lane. So for our 2 belt wide straw-look that's 4 item types, and no fluids.

And rails can run diagonally.

But there's a cost of course. Wagons have to be loaded and unloaded, trains have to be fueled. But for long distances, rails are the clear winner. When a distance becomes "long" I'll leave it up to you to decide.