I've used both the 118 and the 126. Both are fairly good. The Sigalert app can be useful to see how the traffic runs.
One can also use the 23 between Filmore and Moorpark.
Using the 126 to the 5 the traffic around Magic Mountain isn't good, and the road isn't good. If you opt for the 118 there is the Santa Suzanna Pass which is better paved but steeper.
If on the 5 going south, once over the hill its very hard to transition to the 210 because of the high speed non-courteous drivers who don't want you to change lanes.