RE: Newbie questions on broadheads
Readers digest version and I'm sure others will have more to add;
Mechanicals are well liked because they fly like field points without the need to properly tune your bow. That isn't to say that you shouldn't tune your bow properly, mechanicals just fly like field points. They also offer a large cutting diameter which is always nice for large wound channels. When using a mechanical head you'll need to shoot a bow that creates sufficient KE in order for the blades to properly deploy.
Cut on contact fixed blades are nice because they're sharp and do exactly what their name implies; they cut on contact. COC heads allow people with a shorter draw length or a lower pundage bow to acheive better penetration than they would with say mechanicals or chisel tip style heads. COC style heads are usually easily resharpenable.
Chisel tip style fixed blades such as Muzzy offer bone crushing strength. Sometimes harder to tune than mechanicals or COC style heads, they are usually stronger than either style. While you can often times resharpen these head's blades you'll find its often easier just to replace them all together.