I'd probably go with either Polsilver SI or Personna Reds. I can't tell much difference between the two, really. I suppose that, maybe, the Polsilvers beat out the Personnas a little bit on performance, but Personnas win on price. It's a toss-up.
Right now it would be Astra SP. I have tried them in several different razors and they work decently for me in all of them.
However, I still have a two sampler packs to work through as well as wanting to try some that aren't in my samplers like GSBs, Polsilver SI, the various Gillette 7 O'Clocks, and Nacets.
Over the years having used Feather's, Kai's, Personna Platimun, and most in between Derby's give me the most consistent smooth shaves. Personna Platinum's are right on their heels though....