I see many topics come along about selecting the correct jig head for a certain situation or just all around use. There are many factors in this like structure, bottom composition and overall preferences from the individual fisherman. To make things easier here is a base guideline that should help out on picking a jig to match the conditions. Many types and styles will cross into different structures and work in most cases and some really shine in a specific use. Here is a good way to save some time and pick the right head that will do well in these conditions.
Brush Jig
The Brush jig is a great all around jig style. Personally one of my favorites that I fish. This jig functions well in the brush, does well in rock, and light weeds. It also sits the trailer and falls at about a 45 deg angle that has the trailer pointed up.
Football Jig
The good ol football jig. This jig head design works great in rock, ledge fishing, or dragging. Some even use them in brush. The wide football head style runs well through the rock and is very stable from rolling over.
Arky Jig
Arky jigs are a proven design that is very versatile. The Arky jig works good in rock, light weeds, brush, and even skips. It is truly a great all around jig for many applications.
Roundball Jigs
A roundball jig, typically is fished with a finesse skirt on it produces a small profile jig for finicky fish. The round ball jig is a well rounded style that fishes good in pretty much all scenarios except weeds. This jig is one that i resort too when the fishing gets tough and the bite is real light.
Punching jigs/Grass Jigs
This is a jig that makes a great cross between grass fishing in thick weeds in heavy weights to swimming. Its more cone styled head pulls through weeds will less resistance then any other head style above. If your looking to fish heavy weeds with a jig a cone/bullet styled head tends to be the best for minimum weeds.
Swim Jig
The good ol swim jig is a very versatile design and is generally made to mimic baitfish. This design can be fished in pretty much all structures but is best when swimming, light weeds, weedlines, or small rocks, and laydowns. If you cut the skirt it also makes a great finesse jig like the roundball jig. These style jigs have really become popular in the last several years.
I hope this helps in decoding the jig head. There are many styles and many opinions on jigs and how they should be fished. Use this as a base line and grow your technique from there.