I nursed my sons and think I maybe took too long before introducing the sippy, particularly with my first son. He took a LONG time before he was holding the cup himself to drink independently. So I think now is a great time to start with a sippy! I'd just do water in it and let him play with it and get the idea of drinking from it first. Which KIND of sippy I don't think matters a whole lot, as it varies child to child and can also vary as the child gets older, so I'd just get a variety of sippy cups. Some pros and cons to some of them...
The first years with a cap is great because it has a flip cap, doesn't leak a bit so safe with milk and juice in it when out, but it's possible downside is that the liquid comes out pretty slow compared to other sippies.
Playtex is great with no leaks whatsoever, but the cup can never be emptied by the baby drinking it, there's always a little left in the bottom that's stuck there because of how the spout works...not a big deal really though.
The Take and Toss ones are great because they are very cheap and work well, but the tops do tend to come off when thrown, so we now use them for just water or outside.
The nubys are nice with the soft top because similar to a bottle, but they also leak like a bottle when the top is compressed, so a baby that pokes at the top could empty it on themselves...depends on what baby is using it for that to happen. :)
The hard spout nubys I like a lot, no leaks, similar spout to Playtex, so the last little bit doesn't come out when the baby drinks it, but even less than playtex that is stuck in there. I like them a lot and they are only $1 at Walgreens and I'm sure other places too.
The Gerbers are nice and easy to hold, spout is similar to playtex or the hard top nuby so the last little bit is stuck inside. They don't leak a bit, they make ones with 2 handles which is nice in the beginning.
This is probably way more than you wanted to know, but hey, I'd just get a variety of different kinds and start him with water in them. :)