What are you looking for -- price? performance? overclockability? bling?
In general, lower timings are better, but you need to check what voltage was used to get the timings. Higher voltages can result in better timings, but cause the chips to run hotter, so the lower the voltage for a given set of timings, the "better" the inherent quality of the chips (and the more room to overclock them by increasing the voltage). For example:
Corsair XMS2 Pro series:
CM2X1024-6400PRO (5-5-5-12 module) is tested at DDR2-800 5-5-5-12 at 1.9V, and has its SPD (onboard programmed list of timings that motherboard uses to auto-set timings) set at 5-5-5-12 for DDR2-800.
CM2X1024-6400C4PRO (4-4-4-12 module) is tested at DDR2-800 4-4-4-12 at a higher voltage of 2.0V, but has its SPD set at 5-5-5-18 for DDR2-800!
If you just plug each of these 2 modules in without adjusting settings in the BIOS, the first will run at 5-5-5-12 (DDR2-800), while the more expensive, supposedly faster second one will run more slowly(!) at 5-5-5-18 (DDR2-800). It's only by going into the BIOS to adjust the memory voltage to 2.0V and to manually set the timings to 4-4-4-12 that you will get the faster performance from the 2nd module.
Both, however, rate high in bling, having cool flashing LEDs.
Similarly, you'll find that the Ballistix modules are rated at 2.2V!
So, let us know what your goal is for these modules.