
A lot dep0ends on if there are large classes in your breed. In a numerically small breed it can be better to enter both classes as otherwose the pup is in and out the ring before it has had a chance to relaise what has happened. they often show better in the second class :D
I usually do up to 3 classes with mine. At an Open show say breed pouppy class, the AV grpoup class and Puppy stakes. At champ shows I would go for both puppy classes (or puppy and Junior with a slightly older pup) and Puppy stakes.
The mixed breed classes are very good for getting the pup used to being in with different breeds which will stand you in good stead if he goes on to get BOB when older and goes in the Group. Also they are usually seen and moved one at a time, and take a little whicle giving pup a chance to settle before having to perform.