I like to use Farmer's Union European style yoghurt as my starter culture. It contains lactobacillus bulgaricus which gives the taste that I like. One can use any commercial yoghurt as a starter. It is a matter of taste. However, do be aware that commercial yoghurts often have additives for added creaminess. Don't expect your home made yoghurt to have the same texture as your starter yoghurt.
I measure out 6 glasses of milk, add 3 tablespoons of sugar, boil with a vanilla pod. Next, leave the milk to cool till warm. Add 1 glass of yoghurt. Mix well. Leave in yoghurt maker for 15 hours.
I like firm yoghurt so I leave it for 15 hours. If you like softer yoghurt, you can take it out after 10 or 12 hours.
Even without vanilla flavoring the yoghurt is yummy.