Personally I run GReddy Type S and are very happy with them, although the 8kg and 6kg springs do at times when in traffic feel too hard and the car becomes less enjoyable to drive. Get them on a smooth open road and it is smiles all around.
However, my S15 is pretty modded, If you are just going to mod your skyline with mild bolt ons, get somewhere between 250 - 300kw. Drive it mostly on the street with a track day or two through out the year. I HIGHLY recommend TEIN Super Streets. WHY? They are made by an excellent brand - TEIN who only make suspension parts and been in the business for years, 5kg and 4kg springs make for a very comfortable drive around the streets, 16 way damper makes them quite stiff when you want to go for a thrash or have a bit of a drift. And I mean unless you are actually competiting the stiffness is plenty. PRICE - Great value at just under $2000, 2 Year Warrenty, Pillow Ball Tops. For a STREET coil over they really have everything. Their only downside really is they don't go low enough for some people, they go pretty low just not scrub your balls on the road low. I know more than enough people with very fast GTRs running them and not one word of them breaking or having bad performance.
so my recommendation for you are TEIN Super Streets
*Edit* Just noticed you bought HA, good luck with them.