Socialism is more effective at poverty reduction and ensuring the meeting of basic needs than capitalism
The efficiency of the pricing mechanism relies on certain assumptions being met. There are many market failures - information asymmetries, public goods, externalities, lack of enforceable property rights, commonpool resources - that undercut the efficiency of pricing as a method of distribution.
Democracy is flawed.
While it is difficult to make a contention as to the "best," the above objection sets a ludicrous standard of evidence. By the above logic, there can be no evidence for or against any system of governance since none are ever tested under controlled, scientific conditions.