The key thing here is your cadence - the number of strides per minute you are taking. To run for a longer amount of time then as well as your fitness level being the main factor, you can help this by running more efficiently. This can be achieved by running with a high cadence and shortening your stride length.
Have a read of this article about cadence.
A distance running coach I've worked with in the past used to stress the technique he called 'high hips, short levers' was key to having a high cadence. In other words, keep your hips high then at the end of your stride, rapidly bring the heel of your trailing leg up to your backside and rapidly follow through with your knee ready to take your next stride. In other words, spend the least amount of time possible between your trailing leg becoming your leading leg (I know it sounds obvious but try the technique. It keeps your strides relatively short and leg speed high). In relation to your question, this tends to lend itself to your thighs raising more but it also lends itself to your feet moving faster, so in essence, do both. Concentrate on running efficiently and you will start to see speed and endurance results.
Hope this helps