Both with respect to training and handling, how do hanging and standing punchbags compare and what might be the better choice for amateur home use?
Ok, lets take a look at a few aspects of bags and how they might affect various uses.
This is going to range from leather to faux leather all the way down to vinyl. The more you get towards the leather and faux leather, the more tough it will be on the hands, and the tendency of the bag to scrape the knuckles (bag bite) increases. Vinyl is less likely to give these same scrapes, but even off/glancing blows on vinyl will scrape the knuckles. Vinyl will not last as long as leather either.
Winner for your purposes: Probably a vinyl wrap as they are more forgiving and cheaper.
There are three main versions. Hanging, frame, floor. The most versatile is going to be a hanging bag, as it hangs from the ceiling on a chain, allowing for access from all sides without any structure in the way. However, you will need a way to hang a bag that can weigh as much as 150-200 lbs (Depending on style). A frame suspension provides this support for you, but you are limited because the frame will prevent access for certain kicks and movement is limited. It also has a fairly large footprint. A floor standing bag is a better compromise, but it is fairly easy to knock over with more powerful kicks/punches. Most of the floor standing are also water weighted in the base (Although you can pour in sand), so leaks are possible. Also, if you miss a low kick or similar, you are going to smash tender bits on the plastic base.
Winner for your purpose: Hanging if you have the space, otherwise floor.
This is going to vary. Sand, water and air are the most common. A few will have composite tech materials combined with sand. Water is probably one of the better ones, as sand over time will tend to settle and compact towards the bottom, making the lower portion of the bag extremely hard. Good for conditioning, bad for general use. Water is better, but doesn't give quite the feedback that a sand bag will, and if the bladder ruptures you have a mess. Most floor standing bags are going to be foam based fill, which is good but will eventually break down and need replacement.
Winner for your purpose: Foam or contained water.
So overall, for the use that you are describing, a floor standing bag or similar from a company like Century will be your best bet. I would caution that if your son and his friends are going to whack it at will, I would personally recommend some kind of gloves, especially if you end up going with a leather covered type bag. I would also recommend at least a few basic boxing/martial arts classes, as they will teach the proper way to hold the hands/wrists when punching. Even on a softer bag such as a floor model, it's easy to jam/break a wrist because of poor form, or mess up the knuckles punching open hand or similar.