We started out using the baby yoghurt with cereal, but I read the ingredients list and decided to make my own - I like to use organic/biodynamic where I can, so I use the plain BD Farm organic, or Jalna Wholemilk. I think any full-fat yoghurt without artificial sweetners is great for babies. The texture is different in the 2 yoghurts I use, and I prefer Jalna, but BD Farm is a bit cheaper.
I add fruit, and the cereal in the yoplait is polenta, so I add it on occasion, too.
We've also found that a meal we want our Princess to eat which she is not terribly keen on will always go down better with a bit of yoghurt - she loves the stuff.
Another advantage of yoghurt is it's lower lactose levels, so even if your bub is lactose intollerant, their gut can cope with & benefit from yoghurt.