It would be difficult to make a direct comparison. I think Langley is easier, but not by much.
Whitney is 6100 feet of gain in 22 miles. All trail. Whitney is also 500 feet higher, which really counts when you are that high up.
Snow wise you should face similar melt-out times, especially if you take the New Army Pass approach. Via NAP the trip up Langley will be about 5000 feet of gain over 22 miles. With Langley the trail dissipates just below the peak into sandy slopes and boulder-fields. At that point it is a choose your own adventure to the top.
Either way, I think Langley is a fantastic hike. Do it.
