Coilovers are great if you can lower below the legal limit....for shows etc. They are generally better engineered than straight springs and shocks as they are designed as a complete unit. Sometimes it is hard to match the correct spring and shock because a lowered shock may be designed for a 2" lowered spring that has a rating of 300lbs/in. Put a spring that is 280lbs/in and 3" lowered and you won't be working within the specs of the shock.
This is only 'on the limit' stuff, as you will probably get great results just going for spings and shocks.