If you have a single child, and are an avid cyclist, you should seriously consider a Burley Solo trailer. This is a well-made and well-deisgned trailer that, in my opinion, is worth every penny if you are going to use it a lot.
Here are just a few of the features that we love:
1. This is like a Rolls Royce for your kid in terms of comfort. There is plenty of room, and the harness is padded - it looks really comfortable. We take our son for 1+ hour rides, and he has never given any indications of being uncomfortable.
2. Ease of use - we like the quick-release wheels, and it is easy to fold down. We have no problems taking it off one bike and attaching it to another.
3. It doesn't make riding a pain in the rear. Yes, you are lugging your child behind you, and you have to get used to having to account for the space it takes up (ie. when going around parked cars in the road). That being said, I have a lot of fun taking my kid with me on the bike, and I feel that it is a lot safer than the seats that attach to the bike directly.
4. There is space behind your kid in the trailer - this is great for balls to take to the park, and I have even carried bags from the grocery store in it!
There are other features that we also like, such as the tinted windows and ventilation. My son loves it. We love it! I cannot think of any suggestions or improvements that could be made.
One other thing that I would like to note is that the customer service was excellent when I used it. Our trailer did not come with a safety flag. When I called, the gentleman apologized, took our address, and immediately sent a safety flag free of charge. There was no hassle.
I would highly recommend checking out the Burley trailers in general if you are in the market for one!