there is no best. if u want my opinion? go to the local megasuperstore like home depot and go buy potting soil. promix is what i use... http://forum.grasscity.com/showthread.php?s=&threadid=41991&highlight=promix
Im going to have to support wally world here. Wal-mart has miracle grow potting mix for pots, a 2 cubic yard bag or something like that for about 10$, which provides and excelent starter soil. And for transplanting use the same soil - just mix in some bone and blood meal into the soil and let it sit out for a while and your plants should be happy