some searching might help you more, but heres a quick sum up of benefits vs liabilities:
springs:
- decent drop, depending on brand **noooo ebay s**t!!!** get name brand stuff
- will wear out your shocks eventually so these should only be temporary
- cheap, but will get you a good drop..remember you get what you pay for
coilovers:
- may be adjustable
- your suspension will thank you
- pricey, but worth it!
basically, if youre short on funds and just want a temporary drop
with good handling, get "name brand" springs or sleeves.
in the long run, coilovers will be MOST beneficial.
hope this helps