before you arrive you will have a picture in your mind exactly what you want regarding size, build, personality, colour, coat ect and the one that ticks the most box's is the one i'd go for. Just because it's the biggest pup now wont mean it will be the biggest once it finishsed maturing. I like a pup thats well proportioned in all aspects legs, back, feet. I always like to see the sire and bitch and if possible a previous litter offspring but if thats not possible definitly the sire and bitch you should get a good feel for what the pup's will look like.