Meadowbrook is .042 in thickness. Silhouette is .044 in thickness.
.042 is the minimum in my book. For something in .044, you will pay more but I don't feel you need to go higher.
Alcoa made their name in aluminum. I believe they are 'making' their name in vinyl via buying vinyl companies. I'm not certain of this though. Personally, I'd consider both Silhouette and Meadowbrook to be very good based on thickness. It helps when it comes to warping which is your current problem. Do you have foil-faced insulation board underneath the siding? And which way is it facing? And in which state do you live?