I've divided these into three categories: starter sippy cups, standard sippy cups and straw cups. Yes, I've tried this many. I've probably tried more that I have conveniently forgotten too...
Starter cups: the sippy cup that is there to thoroughly confuse your baby who may have just gotten the hang of using a bottle. I don't understand why anyone makes starter sippy cups with a hard spout. That is such a foreign concept to a 6-month-old!
1) NUK/Gerber - These are terrible. For some reason when screwing the lid on, the spout never ends up oriented properly with the handles and it is very confusing for the baby. The hard spout is also not great for beginners. We tried to make these work for awhile, but finally gave up on them.
2) Playtex Sipster - These never worked for my boys. I hoped they would because I think they are kind of cute. I guess cute is not a factor in sippy-cup land. Unfortunately the hard nipple confused my kids and I hate the concept of removable valves that get lost in the dishwasher, get accidentally left off creating a leaky cup, etc. These cups do have the handles attached to the spout which is helpful to babies and they are very sturdy and see-through.
3) Avent - I wanted to be a cool enough mom to rock the Avent stuff. Apparently I am not. I didn't even try these with my younger son, but I remember my oldest son looking at that weird flat spout and then at me as if to say, "what am I supposed to do with this?" It went downhill from there. The benefit to these, I hear from much cooler friends, is that the sippy cup spout piece fits into Klean Kanteen water bottles. All in all, these feel a little over-designed, but I don't have anything truly negative to say about them. I know plenty of people who love them.
4) Nuby - I admit it. I am in love with Nuby sippy cups. For starter cups, the soft tops can't be beat. They feel natural to babies and are sturdy enough to be tossed. They don't have any valves that have to be removed for cleaning and their handles are attached to the spout keeping the whole cup oriented correctly. They aren't perfect, no cup is, but they are the very best starter sippy cup I have found. If you can find them, go for the super spout variety - they are brand new and even better! Since there is less soft plastic on the lid, they are even less likely to spill than the previous design.
Standard sippy cups: the cups your kids will use until you finally come to terms with the fact that they are too old to need a drink attached to them day and night (water only at night, of course).
1) Nuby - Again. Love. My younger son uses these now after going through the worse option of #2 and I'm sure something else which I have blocked out of my mind. These cups are great for the same reasons as the Nuby starters. They are really the least-leaky sippy cup I've ever seen. I love that they are not tattooed with characters also. These are a great cup to move up to after the starter Nuby. The best part about these cups besides their general awesomeness: THEY ARE CHEAP! They cost about $2.50 a piece, which is about $1.50 cheaper than most competing cups.
2) First Years Soft Spout - I bought these as a transition cup for my younger son because they have softer spouts, no removable valves and just seemed promising. They worked great for about a month - long enough for me to acquire MANY of them. Then for some reason, they started leaking both out of the spout and vent AND then out of the threads where the lid is screwed onto the cup. Don't waste your time.
3 & 4) Playtex Insulated Sipster - I used these for quite awhile with my older son between about age 1 and 2. For the most part, we loved them. I have fond memories of taking them on vacation, losing them on vacation, finding drug stores to buy more on vacation. The problem with these is the removable valve. I'm lazy. I didn't like having to remember to remove it and put it back in. The twist-lock cups are basically the same thing, just with this lock-thing on the lid. I really hated that lock on the lid. A few times it took super-human strength to get those lids off. My opinion of these cups is that they are great, very serviceable, if you don't mind those valves.
5) First Years Learning Curve - I resisted these cups for a long time simply due to the fact that they are covered in cartoon characters. However, I finally bought a couple because I was so tired of dealing with the valves of the playtex cups. I was pleasantly surprised to discover that these cups are awesome! We've been using them for about a year-and-a-half now and have always found them sturdy and dependable. I say ignore the ugly designs and go for them above choices 2, 3, & 4.
Sadly, after I have acquired enough of choice 1 for my younger son and choice 5 for my older son, the younger one has decided he ONLY wants to use the same cups as his big brother. See? The sippy cup battle never ends.
...and finally, Straw Cups: those cups you don't have any reason to own but think that somehow they are going to improve your life. My short advice is to save your money and don't buy any of them. However, I'll give a review of the ones we tried when we went on a straw-cup-kick thinking they were definitely better than all of the above choices (why we thought that, I now can't remember).
1) First Years Straw Cup - These. Suck. (and not in a good way) They leak like crazy. Why? It's hard to explain, but basically the little sleeve that holds the straw piece into the cup is also the soft part of the straw that comes out of the cup AND it is also this little plug that acts as a vent. Invariably, the little plug comes out of its hole causing the child to dump the contents of the cup either all over him/herself or the floor. No matter what we tried, we couldn't get that little plug to stay in its hole.
2 & 3) Playtex Twist-Lock - These don't leak but they are ridiculously complicated and the straw doesn't touch the bottom of the cup, so there's no way to get all the liquid out. Both my kids find these frustrating.
4) Nuby Handle Straw - (They make this in an older-toddler cup without handles too) This cup is great - no surprise that it is Nuby once again. It has never leaked, is not overly complicated and works well. The only problem I have with this cup is that babies young enough to need a handled cup, don't quite understand the fact that you don't need to tip up a straw cup. I don't understand why a straw cup is needed for this age group. Nevertheless, if you feel like you must get a straw cup, get one of these (handle or no).
So there you go. That is my take on sippy cups. To sum it up:
~~Nuby. I can't say enough good things about these cups. They are well-designed both aesthetically and functionally. They are inexpensive making the investment of 7 or 8 not quite such a huge deal.
~~For young babies, go for a soft spout and handles attached to the lid.
~~For older babies/toddlers, go for the sturdiest cup you can find that is easy to wash, has no nooks/crannies for rotten milk to hide in and has a valve system that is integrated.
~~Consider where you will be using sippy cups (at home on carpets, on the go in carseats, out on hikes, etc.). You may need to grab a couple of different kinds.
~~Decide what your *rules* are for sippy cup use. We are pretty free and easy with drinks around here, we just limit juice consumption. If you are an only-at-the-table parent, then you probably don't care so much about leakage.
PS: Oh, and photo credit goes to BabiesRUs, Amazon, and I think Target.