lower latency at higher speed is what you want. for example, 5-5-5 is worse than 4-4-4 for ddr800. however, due to limitation of ram and the technology itself, the latencies must increase at higher clock speeds. so, 5-5-5 for ddr1066 is good. and yes you want smaller numbers for the timings
you can also judge ram by the rated voltage for whatever advertised speed. i.e. ram that is only ddr800 and 5-5-5 timings with 1.8v could probably do 4-4-4 with 2.0 or 2.1v.
when comparing ram, first compare speed (obviously). then compare latency timings to see which is lowest, and lastly check to see which ram operates at the lowest voltage. that formula will lead to the best oc potential.