Decriminalization:

While the tenets of decriminalization change depending upon how one decriminalizes a commodity or commodities, the basic statute is that decriminalization removes incarceration offenses from the commodity or commodities it affects. Sometimes that means that those caught with the offending commodity have their goods confiscated and a fine applied. Sometimes it means that they can carry a small amount of the commodity in question. Never has decriminalization allowed unlimited possession of whatever commodity it targets, nor the sale of said commodity.

Regulation:
Regulation also varies in meaning, but the core tenets are an unlimited amount of the targeted commodity/commodities regarding possession. Sale is allowed but only under certain restrictions (such as inspection of goods, license to sell, etc). The debate for regulation is the restrictions it imposes on the sale of a commodity or commodities in order to control said sale by a governing body, often the government of the country allowing this law. Regulation can also impose taxes on price and the companies selling the commodity or commodities or set age limits and similar restrictions upon sale.

By the way, feel free to revise my definitions of regulation and decriminalization.

After this, what normally occurs is the "What constitutes misuse of the commodity in question?" question being debated and restrictions applied regarding where/when/how the commodity is to be used.

The question is, which would be a better method of legalizing drugs? Please do not respond in accordance with which is more popular at the moment but rather of which would be more effective in dealing with current legislation on drug use and sale.