there is competition even among the minibus queues. Two services go to Lopburi, one is from the Victory Monument circle, the other is parked under the expressway. While they both go to town, the one under the expressway charges a little extra to bring you to the military gate at Saotong. They park at the PTT petrol station on the corner, and I believe the first service in the morning starts at 4 am.
They are convenient and go the back route through Bang Pahan, while the regular bus service goes through Saraburi. What I do not like about them is, they are almost always on the wrong side of the road, and I'm sure you know how many blind corners there are between Lopburi and Bang Pahan...

The Hua Hin route is more straightforward, so I'd suspect the big bus is the better option. Not sure if they operate a few services out of Morchid, though I know the Eastern seaboard is serviced by both Ekkamai and Morchid. There is competition among these operators, too.
Many years ago, I had to go to Chiangmai practically weekly and would take the overnight VIP bus. Several companies did this route, and they were not created equal... I found my favourite and could even do a phone booking (except for major public holidays).
Hobie,
I don't know how you preserve your sanity by driving yourself. Most of the drivers on the roads these days send me around the bend...
My two cents.