M.,
My suggestion, from years working with families and a lot of indepth training on the subject, is skip the sippy. If you DO go with a sippy, get the old fashioned ones that don't have the straw, no-spill nozzles, etc. Here's why:
Your child is capable of using a regular cup now with a little help from you. He'll catch on quickly.
There's a lot of evidence linking over-use of sippy's with delayed speech development because the sucking on the no-spill sippy is no different than that of a bottle. The motions required to use a regular cup develops the oral muscles needed for continued speech development.
New evidence links sippy cups with increased tooth decay. Put simply, kids sip on a sippy all day, and give the bacteria that rot your teeth a constant food supply (unless you use water only).
I understand the difficulty with the messes and spills when it comes to cup learning (my 15 mo dd has been using a cup since 4 mo with my help, and it takes patience and time.) But it's a myth that a sippy cup is necessary to make that transition! At meals, give him a regular cup, with a couple of sips of water at a time, and help him figure out how to use it. Then he only gets wet if he spills.
So much luck to you!!
H.