We've come a long way since we were digging with our hands way back when to the gardening spade that we use today. Only the quality of the materials have changed since the Chinese had a bronze spade that closely resembled today's spade around 1100 B.C.
Gardening spades are workaholics and because of the nature of the work they do, it's counterproductive to not buy the best one you can afford. Buying look alike garden tools will just frustrate you and adds to our landfills.
With all that said, let's start with the head of the spade. The shape of the spade's leading edge can help you immensely depending on your soil type. A deeply dished blade (usually found on a shovel) will speed up the process of moving loose materials.
Slightly Rounded Leading Edge - This is the most common garden spade and works well in most soils.
Pointed Leading Edge - The point or points help greatly in rocky soils as the points deflect away from smaller rocks. The point also makes it easier to push into any type of soil.
Narrow Blade - The narrow blade spade are great for digging in confined spaces as well as digging ditches.
Slotted Blade - The slotted blade is made to have less friction going into the ground in sticky clay soils.
Let's talk handles. Ash hardwood handles have been the standard for hundreds of years, not only for their durability, but the ability to absorb shock and vibration. Fiberglass handles are stronger, but absorb less shock and are harder to fit into the socket should it break and need to be replaced. Steel handles are very durable, but heavy...some gardeners like the added weight for digging.
Spade handles come in a variety of shapes and lengths with "T" handles being the most popular. "D" and Bulb End handles are also quit popular, but what it comes down to is personal preference. Also, when choosing the length, remember that spade is a lot shorter when the blade is in the soil. Using a spade that is too short is likely to strain your back and make gardening less enjoyable.***Spade Head Size - Most people (including me) automatically choose the largest blade size they can buy. We think that we can get more done with the larger size, but in reality we're only tiring ourselves too sooner...not to mention the back pain involved using a large tool. Many gardeners are opting to use the smaller border size spade. It makes for a lot less back pain, less tiresome and more enjoyable gardening. -Just something for you to think about.