Never never buy feminized seeds. Why? Female plants are sprayed with silver thiosulfate solution to turn them into hermaphrodites that will produce all female seeds when you use their pollen on a female plant. This is fine and dandy, except that these seeds are going to be very sensitive to stress. They will likely turn hermaphroditic themselves and produce seeds which you do not want when growing marijuana to smoke. As little as a brief power outage can be enough to send your plant into hermaphroditic mode. Seeds take away from potency and yield by roughly 30%.
Cloning is the go to option because it can be done to multiple degrees of intensity and has a lot of opportunity. You keep one female plant that you think is really good to take your clones from. Be sure that you NEVER send your mother plant into flowering mode. Only in some special circumstances can you take clones from a flowering plant, but then you will have to get a new mother all over which sucks if you have picked out a mother you thought was better than the rest and just get rid of it… Keep your pretty plant from flowering by never switching its light pattern, so cloning is not an option if you are growing outside. Each plant you clone from the mother will be an exact replica.