Here's my $.02 worth:
Cylinder rod stock in 1045 or 1050 makes great pins for most applications. It is:
Weldable if you need to weld a head on it
Considerably tougher than plain 1020 round bar,
Very accurately sized, which is important for some things,
Very, very smooth, which gar-max graphite bushings demand but all bushings like.
Pretty cheap and very easy to find. Most shops that repair cylinders have bent rods that you can cut up into pins. Most steel suppliers carry it.
The chrome plating stalls off rust for a year or two.
Ag loaders and industrial loaders/backhoes are a lot different. Lots of ag loaders are horribly underdesigned, have tiny pins and sometimes not even replaceable wear bushings. Improving them is like hot-rodding a flathead v8--anything you change will probably be a big improvement.
If you are reworking something and the pins you're taking out are really hard, be very cautious about replacing them with softer/weaker stuff. If the manufacturer popped that kind of money, it usually indicates that cheaper stuff didn't work, and it was too late to redesign it. Fancy heat-treated alloy steels used as pin are usually a crutch for a poor design. There are valid reasons to use high-strength, expensive materials, but most of them exist only on airplanes or race cars.
Replaceable wear bushings are great. Connex or Vogelsang spring-steel bushings are probably the easiest to use--they drive in with normal tools, and are cheap. They do require grease.
Gar-Max filament-wound graphite bushings are amazing, and do NOT require grease. They DO require very accurate bores and very smooth pins, and they don't like hammering impact loads.
No wear bushings at all is cheap to manufacture. It has no other advantages.
If the pin is "full-floating", where it's free to turn in all of its holes, retaining it is simple--cotter pins, roll pins, snap rings, or bolts and nuts all work fine.
If the pin is designed to be anchored down so it doesn't turn, be careful about how you do that--look at some current Deere and Cat heavy equipment to see how they keep the pin from rotating or working out, but still allow it to wiggle around when the pin flexes. They don't (very often) just stick a bolt through the pin head anymore. If you are seeing pin heads sheared off, retaining bolts breaking or constantly working loose, or previously-applied field fixes where the pin head is welded down, you're probably looking at an underdesigned pin joint where the pin or the surrounding structure is flexing a lot, or where the lubrication is breaking down and the pin is seizing in its bushing and turning. When the loader boom is grabbing the pin and trying to turn it, you aren't going to stop it with a 5/16 bolt. Sometimes, when those problems are chronic, it improves things to just give up and let the pin float. Yes, it will eventually wear out the holes in the frame, but that's often preferable to the pins falling out.
PITA. I could be wrong but that's what I remember.