coilovers are great for getting the correct stance, but the ride quality will suffer IE it will be harder than a separate shock and spring set up.
Just springs - not sure if its the same on the leons but on the astras doing a drop of around 30-40mm on standard shocks is fine, it will give better handling, better looks and minimal loss in ride quality. However if you drop it more than that on just springs IE 50mm then it is worth while changing the shocks as well, as the standard ones will suffer from the constant pressure of the
lower springs.
Upgraded springs and shocks - arguably the best way to achieve a similar ride to standard but with greatly improved handling and looks.
Looks like the common ones are:
Eibachs Pro kit -
lower 30mm springs only
Eibachs Streetline kit - lowers up to 50mm
H&R's - lowers 40mm
For shocks it seems the koni FSd's are the popular choice.
I will be going for the eibach streetline kit with uprated dampers but not sure which as yet.