Interesting question, but not that hard to figure out. First, from an chronological analysis, the shocks on a car generally wear out before the springs, so replacing the shocks first would be logical.

There is also the experience of some members here that using shorter springs on OEM shocks causes the shocks to wear out faster (valving not designed for the shorter stroke length), so if you run lower springs, you'll need to replace the OEM shocks in an accelerated amount of time.

Unless you're getting an extremely good deal on either the springs or shocks, is there any harm in banking the bucks and waiting until you can do both, and maybe add larger anti-roll bars and a camber kit, at the same time?