Firstly, if your car says to use 5W-30, then use it.
The difference is basically that 10W-30 uses a thicker base oil but less additives. Yes, there is more friction at start-up using 10W-30. But there is also more shearing using 5W-30 and up until the late 1990s, many lubrication guides/car manuals stated that 10W-30 should be used for "extended highway driving" largely because of 5W-30 shearing down to a 20 weight. However, 5W-30s are vastly improved and this isn't as true as it once was and 5W-20 will protect most engines adequately anyways. But 10W-30 may still be ideal with some applications where it is called for due to higher operating temperatures or constant summer highway driving...