high tech because of the color's and growth you can get out of plants..
co2 is a little riskier if you don't know what you are doing, but you cannot make a low tech setup look as good as a co2 setup.. especially with plant setups like iwagumi etc..
Not to mention how co2 helps prevent most algae.. if you know what you are doing.. I haven't seen too many low tech tanks that haven't had problems with BBA amongst other massive algae problems
Not sure what Rexthecrayfish meant, but take a look at a high tech co2 system, a low tech doesn't compare period