I bought the "Extra small" size for my boston terrier for his very first toy... it was a perfect size for him, considering he was 2.5 pounds.  He still plays with it, even though it can fit entirely in his mouth... I have bought the "small" frog and he was unable to destroy it for about 4-5 weeks (which is the longest lasting toy to date).  Now that he is fully grown, I have purchased the "Medium" Teddy Bear, and he still plays with it roughly.  They are great since you can give it to them without a squeaker so he doesn't try as hard to destroy it in hopes of obtaining the squeaker!  It is hard finding dog toys that are soft and don't have squeakers! Judging by the size of this toy, I wouldn't think it should be given to a dog over 25-30 pounds.