Vitamins increase EVs in a particular stat by 10 for the first 100 EVs in that stat. As far as your question is concerned, vitamins are worth it depending on the person. It is I believe 98,000 pokedollars for 10 vitamins, so if you have money to spend, it's your choice. Horde training gives 5 EVs for the stat the Pokemon encountered gives, and us given throughout your party via EXP share. Super training and vitamins train certain stats well, but for a single Pokemon. Wings also exist, giving 1 EV for a certain stat, but I don't know how or where to get them. Long answer short, it's your decision on how to train. Hope I helped!