I’ve done Amtrak from LA a couple of times, and it’s a nice way to cut down on the driving stress. Driving 2.5-3 hours twice daily is grueling, especially when it overlaps with rush hour. Plus you have time to read your new comics on the way home!
But it does lock down your schedule a bit on the days you take it, and the line to get on the last northbound train of the evening is…actually not too much worse than some other comic-con lines, now that I think about it.