Here is a random counter-intuitive fact about chemistry: while the atomic weight of hydrogen is 1.00794 grams per mole and that of helium is 4.002602 grams per mole, the helium nonetheless has 92.64% of the buoyancy of the hydrogen. This is because air weighs about 1.3 grams per litre, while hydrogen and helium gasses weigh 0.08988 and 0.1786 respectively. It is the difference between the density of air and the lift gas that is important and, in absolute terms, hydrogen and helium are not that different.
Ultimately, both hydrogen and helium are capable of providing about 1kg worth of lift per cubic metre of gas at room temperature and pressure. The major reason for which helium is popular as a lifting agent for balloons and zeppelins is because it is not flammable (it is actually a remarkable unreactive element). Unfortunately, helium is a lot more costly, has other uses (such as cooling superconductors), and is in the midst of significant shortage.