A cross breed has just as many health problems as the pedigree parents. A pug cross cannot be guaranteed not to have breathing difficulties - I bet if you asked the 'breeder' of these puppies if they would put that statement in a written guarantee you would not see them for dust!!!
If you do buy a cross breed then make sure both the parents have authentic certificates for any health problems for that particular breed.
Although if you want a cross breed why not visit a good rescue centre like the Blue Cross etc. They have lots of puppies/litters available and at least you know that any money you hand over is going to rescue other dogs and not into someones pocket.
http://www.freewebs.com/manytearsrescue/dogslo okingforhomes.htm
As regards choosing a particular puppy out of a litter this has some good advice:
http://www.simplysarah.com/puppiesselect.asp
Always remember to follow your head and not your heart and make sure your resident dog will get along with the pup and will not feel jealous and left out.
Oh - and if you decide to get a bitch then make sure you know how to cope with her first season - especially if your dog has not been neutred!