I like 5" sheild cut myself. 5" length in case I have a bad release or other goof--they will stabilize my arrow quicker.I just like the sheild cut. Hopefully I won't goof up so bad that I'll need a 5.5" or high back cut--these are noisier. Some folks do just fine with a 4". Parabolic is generally the quietest cut, but sheilds aren't very noisy. Just do a little tinkering and see what works best for you.

Chad