I've got the small one and the huge horse size one!!
The large one is better for the labs and the small one is better for the spaniels.
I paid £15 for my small one and I got a bargain at £18 for the large one, they usually retail at about £35. I got them both from e-bay. It took me about eight attempts to get a large one but they are always available.
They are great for my goldens who shed practically all year round. They are worth every penbny you spend on them!!
I bought mine from QVC - large... the blue one. Was £30 ish.
I'd personally say the small one would be fine. Having used it... its pretty heavy and really and truelly... you don't need all that size. If I was buying it again, I'd save myself the dosh and go for a small.