Pregabalin; hands down. In my opinion, pregabalin (Lyrica) is good for a few reasons. First of all, unlike phenibut, pregabalin is regulated medicine, so you know what you're getting every time. It's better than gabapentin (Neurontin) because unlike gabapentin, it's bioavailability/potency is not mediated by stomach content. Gabapentin's effects tend to vary wildly based upon the lipid content of your stomach. Otherwise though, pregabalin and gabapentin are quite similar in effect.
Second of all, I've heard some relatively bad things about phenibut through reading people's experience with the substance. I've only used it a handful of times, so I cannot personally comment on the dependence side of it, but from what I've gathered, phenibut dependence and withdrawal (which is usually described in nightmarish terms) comes on quickly.
Pregabalin dependence/withdrawal seems to be quite severe as well in some cases, but it seems that most of those who experience severe withdrawal have been on the medication for a long period of time. So in conclusion, pregabalin takes the cake. It's an awesome medication when used sparingly. I am clean from opiates currently and the pregabalin tends to give me the little boost I need.
This is all purely opinion. I'm sure other BL'ers have different preferences.