The garden trowel blade you should choose comes down to the job you choose to do and the material it is made from.
The best material to choose for your garden trowel blade would be stainless steel. This is because it is lightweight but still strong enough to dig in hard soil.
Another important consideration to make is whether or not the blade has been coated. Some garden trowel blades can be zinc chrome plated which makes them more corrosion resistant and able to resist wet, heavy soil.