I have whole cupboard-full of different types of sippy cups from when my first child was little. He refused the bottle at about 4 months old, so I was on a desperate hunt for a cup that he could use. The ones that didn't work at that age I did use later on, so here is my two cents on the different brands and types.
Kleen Kanteen Stainless Steel Sippy
I would love to have more of these cups, but they are more on the expensive side. They are nice because they are stainless steel and I feel better about throwing them in the dishwasher. The stainless steel doesn't hold the smells and tastes of the drinks like plastic sometimes does. Plus they last forever, and you can different tops for when they get older.
Born Free Training Cups
These are great cups too. They don’t leak (the spouts for older kids do drip), they are made from 'safe' plastic, and the spouts are softer so it’s an easy transition from breast to sippy cup. This was the only thing my son would use after he refused bottles. You can take the handle off and it's more like a bottle. The only bad thing is, in my opinion, that there are so many parts to clean, kind of a hassle.You can buy different spouts if they get chewed up, or to move up to the next age level.
Playtex The First Sipster
I have a couple of these too, they are smaller size, easier for baby to grab, and less parts to wash. They don’t leak at all (until they have been overused by a 2 year old and the spout hole is all chewed up). They are also pretty inexpensive and easy to find in stores.
Kid Basix The Safe Sippy
This is another stainless steel one, and more costly. This is better for older toddlers because of the size, shape, and type of spout. We use this one a lot now, but it does drip if upside down. It’s pretty easy to clean and indestructible. It's supposed to be a safer spout.