The Pro-kit drops about 1.2-1.5", and the Sportline drops about 2.0". It just kind of depends on how low you want to go.

The lower you go, the more harsh the ride can become (generally) and you'll have more camber problems (can be corrected with camber kits). With either setup, you'd be best off to match the springs with performance shocks (Koni, Tokico, Bilstein, etc) to maximize handling and they'll handle the added stress of lowering, slightly stiffer springs etc better than stock. Some higher end ones have dampening/rebound adjustment to allow you some adjustment to make it more like you want it ride. With the Sportline you pretty much want performance shocks. With the Prokits, you could get away with stock shocks for a while if you had to. I used H&R sports from miles 30K to 55K on my 99 Accord and the stock shocks held up fine. I've since replaced them with Koni's and it's considerably better handling wise.

Cheapest: Prokits (or other mild sport springs) with stock shocks.

Best: Springs mated to performance shocks OR a complete coilover system that has the spring and shock integrated as one (this usually has the added benefit of height adjustability...Tein, Apexi, etc).