Tirz is better, fewer sides, maybe 15% more weíght loss, and the additional health benefits (liver fat clearing etc) are stronger. BUT, Tirz dosages are MUCH higher making it an expensive proposition. One vial of Sema, starting at .5mg (yes, as a male .5mg should be the starting dose, .25 is a waste of time for males), and if everything works out, you only need two weeks at that dose before going to 1mg where you'll start to see results. So 1 5mg vial will last 5 weeks. Tirz minimum is 2.5mg (10x as much!) and again, useless for males till you hit 5mg. So really it's one lousy dose for an entire vial. Max dose for Sema is 2.4mg vs 15mg for Tirz! Two doses per 5mg vial vs 3 vials for ONE Tirz dose!
You can always switch from Sema to Tirz, but going the other way not so much.