As above, depends what you want, and what you are prepared to put up with.
Coilys are a LOT harder than normal suspension, but will give and edge grip wise when set up correctly in certain conditions.
I've always found the combo of Koni adjustable with avo/chassis dynamics springs work exceptionally well, although others prefer ahmed springs which are an excellent choice, I'd happily use either, just prefer the avo myself, but use coilys anyway.
My advice is to try and get a few rides is cossies with different set ups, so you know how they will be before parting with money, even if it takes a few months.
tabetha