Best fermentation temperature mainly depends upon three things. Which yeast you are using, the original gravity of the wort, and the taste of the finished product you are aiming for. First place to start would be the specifications sheet of your yeast for the best recommended temperature range. Do you want more or less esters in your beer. Brewing at the high end of the temperature range produces more esters. Active fermentation produces heat. You can expect a temperature rise of 5° to 10° depending upon the yeast pitched and the volume of yeast pitched.