So, I have answered this before, but in a more general sense. The USB 3.0 physical connector ONLY uses the USB 2.0 portion of the assembly for power supply, so there is no reason, at the connector, that one type would charge faster or slower, from a standards basis.
HOWEVER... after a little research, I discovered this: Virtually all data signal wires within the cable are 28 gauge, in both 2.0 and 3.0 cables. Power wires, OTOH, were always 24 gauge in 3.0 cables (at least in the sources I found), and were one of 28, 24 or 20 gauge in the vast majority of the available 2.0 cabling.
We can make some reasonable assumption that a higher gauge (and thus thinner) wire is going to provide more resistance and thus less current flow (assuming the copper is of comparable purity in each gauge). So, it is also reasonable to assume some 2.0 cables will charge slower than the provided 3.0 cable, and some 2.0 cables will charge faster. And, given identical cable construction, a longer cable will attenuate the power more than a shorter one, also providing a slower charging pace.
Summarizing, given a charging brick of constant amperage, a higher quality cable will charge faster than a lower quality one, as the higher quality cables will tend toward lower gauge power wires. And, it is true that most, if not all 3.0 cables seem to be assembed with power wires that are lower gauge than at least some of the 2.0 cables on the market, meaning that you will probably always get reasonable charging performance from a 3.0 cable in good condition.
Simply put: spend a little extra money on cables of whichever standard you choose, and you will reap the benefits when charging.
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