As long as you can mount the scope far enough forward to get good eye relief the height is more important than the style you choose.
A cantilever mount is needed on an AR-15 in order to get the scope far enough forward that you get good eye relief without using the forend rail to mount to. You don't want to use the rail on the forend (of an AR-15) because it's a separate piece which could potentially induce accuracy problems. On the ACR you have a solid one piece rail the entire length so a cantilever mound is not needed.
It's up to you, I have a Burris PEPR on my ACR and it works well. A one piece base like a PEPR or other cantilever mount will typically be a little heavier but I try not to let a couple grams make my decisions for me.