Really hard to answer that. Take a look at what we all think on the posts at the top of this thread. I read these when I was starting up and decided on Tesco Purple bag muesli and/or Exel nuggets. I think it's pretty universal that piggies never seem to eat 'all' of the muesli bits, they pick out the bits they like first, then nibble at the rest, and leave what they hate.
The argument for nuggets is a good one. They get all the nourishment they need in one nugget, so can't be selective. But then if they won't eat the nuggets.....
Are you as confused as the rest of us now? lol
Seriously though, the threads at the top will tell you about people's experiences with different dry foods. xx