I use whatever springs I have, although right now I need to get some softer springs and so will be getting lab ones, simply because they are cheapest, they have the most sensible range too, a lot like the HPI range but a little more regularly spaced. Suppose for once being in the UK has it's advantages, seeing as we can get lots more parts for the lab easily.
A word of warning, after recently fitting the titanium turnbuckles to my car I've found the small clip on ball cups used for some links tend to stretch too much. You get a white ring around them where the turnbuckle stops and they get very weak. I'll have to ask Modeltech about this, seems like I'll have trouble with the bottom steering linkages, which luckily I didn't change over yet since I didn't want to ruin my setup (ok ok I'm lazy too)
Just back from my first night using my new KO Vantage 2 radio which I got second hand, being able to adjust the amount of steering is very very useful, especially on the lab. Unfortunatly the wooden gym floor was incredibly dusty tonight so even with new radio I was sliding everywhere.