Pslin was the strongest I have tried by far. Recompadrol is def my #2 and for the price it is crazy...lots of proven ingredients including berberine and banaba at 20% corosolic acid. Right now I just cap my own mix of berberine, gymnema (75%), and banaba (2%). This combo works much better than several name brand GDAs that I have tried and might be up there with recompadrol for me, but the hassle of capping it all is a factor (and if you don't cap it, banaba and gynema taste fine, but berberine has a long-lingerine bitterness that takes forever to go away).
Honestly it is a trial and error process as everyone has their preferences. On this board, though, the overall most recommended from all the threads I read is Recompadrol, so you could start by going with the popular consensus and try that. Cheap, effective, and everyone lists it as their top GDA or one of their top GDAs so hard to go wrong with it.