Our son has tried a few sippie cups and we definitely have our favorites. As a first time-buyer of sippie cups, the choices can be overwhelming and confusing. Here is our summary of the cups we have experience with, which hopefully will help.
Gerber Graduates Fun Grips Soft Starter: This was our favorite starter cup. It has a soft spout and really is leakproof. We started using it when our son was 6 months, and it is still in use today and he is almost 2 years. The only bad thing about it is the capacity is 6 ounces and a 2 year old drinks that pretty quickly. It is a good starter size though, because anything larger would be too heavy to train with.
Playtex Lil' Gripper Spout Cup: We really like this cup for our toddler. It is spillproof, really durable, and it has a great capacity.
Playtex Insulator Cups: This is the same cup as above, but it is insulated, which is said to keep cold items cold twice as long. This insulating factor also keeps it from sweating. According to the Playtex website, both cups are 9 oz, but it seems to me that the insulated one has a smaller capacity. The other thing I don't like about this one, is that you can't see through it to see how full/empty it is, but I guess there is no way around that with an insulated cup.
Gerber Fun Grips: Some models change colors with cold temperature and it has the same spill-proof stopper as the Gerber Graduates cup mentioned above. It has a great capacity for sippy-cup pros. I really like this one.
Take 'N Toss: These cups are really cheap and we like them. They aren't spillproof and liquid flies when shaken, but they are great to have around as water cups, or when dishes get a little behind and you supervise your little one while he drinks. These are great to take on trips because they are easy to handwash since they don't have the valves that usually require dishwashers to clean, or they are disposable. Note: Usually when I go on trips, I take a small bottle of dish soap and a bottle brush so I can wash baby cups in the sink.
Munchkin Mighty Grip: This is a great trainer cup, but it doesn't last through the long-haul without having to replace the nipple-like top. My son liked to chew on it and he eventually bit a hole between the two slits, so now it quite a bit less spillproof.
Munchkin Straw Cup: We don't particularly care for this one. The straw is two pieces, and when you put it in the dishwasher basket, you have to spend time to stick it through the tight holes which is more effort than we particularly like to put forth. My almost two year old can't seem to open the top valve by himself, but he sure likes to close it, which once again is extra unnecessary parental effort. The top valve (the orange piece in the picture) has a hard time coming clean in the dishwasher, as does the lid sometimes. The area within the lid somehow always gets liquid in it and spills. We avoid using this cup altogether.
Here is another sippy-cup comparison that is a bit more technical.
Emily became a mommy on her birthday in July of 2008 to a wonderful son named Sam. She has since become rather obsessed with all things related to babies and baby items.