Manners has taken the shooting community by storm lately. They have a fantastic product, but with the amount of backorders the have, quality control can suffer as a result. Out of the 6-8 stocks I have purchased from them in the last 2 years, 3 of them have had slight cosmetic issues that had to be addressed. McMillan has a rock solid product that just flat out works and very rarely has QC issues. The main reason I go with manners is the rigidity in their stocks. Mcmillan's seem to have a little more flex in them. Just be prepared for longer wait times, and possibly some cosmetic issues (most likely not). Either way it's really up to your personal preference on ergonomics and colors. Both are great products. The only gripe I have these days are the price of them.
***, some of the stocks cost as much as a custom action??????
Both are top tier. I use Manners and love em. If I started with McMillan, I would probably be a McMillan fan instead of Manners. I love the EH-1 and EH-2 from Manners. Can't go wrong with either.