Cones are the one must have (other than players and a ball) for practice and training.  They can be used to represent field markings, goals, obstacles, space markers, etc.  There are several types of cones available, each with their own pros and cons.

Discs

Discs are the most common type of cones.  There are a variety of sizes, but most are about 8 inches or about 12 inches.  Discs are light weight, soft, and mostly flat.  They ideal as field and space markers because don’t interfere with the ball or the player.  They are crushable and will survive most practice drills.  Discs are available as a variety of colors and are the least expensive variety.

On the down side, they are very light.  They are easily kicked out of position and often moved by the wind.  They are almost flat, so they can be hard to see from across the field or as goals.

Domes

These cones are taller, heavier and stiffer.  They work well for most of the same purposes as disc cones, but can be more obtrusive when used as field markers.  They are far less likely to blow away in the wind.  Some varieties of dome cones are weighted and designed to hold poles or flags. 

Unfortunately, the stiff nature of these cones makes them more brittle.  They tend to crack and break if they are stepped on.  It is unlikely that they would survive a lawn mower.

Pylons

Pylons are scaled down versions of the traditional traffic cone.  They are available in a variety from small crushable cones to the full size traffic cones.  They are easier to see and work well for corner markers and goals.  Depending on styles they can be light weight or quite heavy.  Pylons are generally the most expensive variety of cones, but it is unlikely that you will need many.