My opinion on this changes, but here's my two cents:
3.7 volts (normal e-cigs): My Freedom Smokes 24mg Double Flavor RY4, hands down. Nothing comes close.
5 volts or higher: Puresmoker Riskee Yuice
Might just be me. I absolutely love the MFS flavors at 3.7 volts, but it's too much at 5+.
NOTE: I don't think I've ever had anyone's RY4 and said "wow this sucks". Every RY4 I've tried from everyone has been very good, and I've tried a lot of it.