If one is that pressed for space your packing wrong.
This is actually an important point. And I would add that if you cannot fit a proper shovel in your vehicle, it is time to re-prioritize the equipment list.
It is easy to fill a truck with equipment, add a roof rack and fill that, and then pull a trailer filled with additional equipment, yet forget the most important tools required on a trip. I often find travelers in remote areas that are completely unprepared to repair or recover their vehicle, yet have every piece of camping equipment they can stuff in the truck.
Unfortunately, tools like a shovel, proper jack, a full-size spare, etc. are often neglected.
For a shovel to be effective, it must be a high-quality, sturdy implement. The cheap folding shovels only lasts minutes of work, soon followed by the person wielding it, as the effort and ergonomics of using these compact units are exhausting. Doing just one serious road repair will put a good shovel on your list of required gear.
Selecting a proper shovel:
1. D or T handle, which aids in leverage and reduces fatigue. Avoid wood Y handles, as they can split under heavy loads or leverage.
2. Length. Length has less to do with fitting it in your vehicle than fitting you. I recommend a short handled shovel that with the point touching the ground, the handle rests in your hand, with the arms down and in a relaxed position. A tall person with too short of a shovel will tire quickly. At 6'1", a 37" long shovel is perfect for me. If you can fit a longer shovel easily, do it. Ash or fiberglass make for a good handle. Wood handles should be cared for to prevent drying out, splitting, etc.
3. Blade. Use a round-nosed spade, made from carbon steel. The blade should be somewhere around 8-9 inches wide, and 10-11 inches long. Too narrow, and you move too little material. Too wide, and you move too much (i.e. too heavy) or you cannot maneuver the blade around a tire, the undercarriage, etc. The steel should be in the 12-14 gauge range.
For the last ten years, I have used a good-quality, tempered shovel like this:
These are reasonably priced shovels, and have proven durable through years of use. Lowes typically carries shovels like this.
Mounted to the Tacoma like this:
This type of mount makes accessing the shovel very convenient, but did expose the rack and tools to trail damage and weathering/rust.
On the Defenders, there are clean, solid mounts like this:
A mount like that could be adapted to most flat surfaces. QuickFists are also effective for mounting a shovel. If the shovel is inside, just make sure it is mounted solid should an accident or roll-over occur.
Recently, I have used the Carters shovel, which I first found on the Expedition Exchange site.
It is well-built, with a thick blade (the thickest I have seen on a short shovel). The blade is also angled more parallel with the handle and the dish of the blade is more shallow, which should make it easier to dig under frame rails, axles, etc. I used this shovel extensively in Guatemala, and found it very durable.
If you do need a folding shovel, I have found the Hi-Lift Handle-All to work ok. The segmented handle is not very comfortable to use, but at least it is long enough and durable. You also gain the benefit of other tools in the kit, like a felling axe and a pick. I would leave the heavy sledge in the shop...
That is about all I have to say about shovels