Some other threads regarding trailers:

http://www.bikeforums.net/showthread.php?t=126690
http://www.bikeforums.net/showthread.php?t=148590

I personally have a cycletote and have had a Burley. I do not ride with the kids much in the rain but on the two occasions where I was in mixed rain/wet weather (3+ hours), they stayed dry. I think the fabric on the cycletote beats any of the other trailers I have seen by a wide margin, Cordura vs. Nylon. I think the other carriers have better integration of water/weather proofing into their shells, but the Cycletote has never not performed well for the conditions I have been in. I do remember reading of one satisfied Cycletote owner in Seattle. One thing that cycletote does have that the others do not is a piece of fabric that can be attached and detached from the hitching arm that acts like a fender. This fabric block is very effective at keeping road spray off the trailer which decreases the likelihood of water penetration and alos helps keep the view area clear for the kids. A fender would accomplish the same task but you may not have one on your road frame. I think almost any of the name brand trailers will do fine with weather tightness. With that in mind you can look to other features to help you decide on what would fit your needs. Another positive note for the Cycletote was the availability of replacement fabric. Our Burley fabric wore out. Trying to find someplace that would even get the fabric for us was difficult enough but the fact that it cost almost as much as a new trailer pushed me over the edge. My cycletote has had 3 years of rough handling and that fabric has not failed yet. Plus I know I can get a replacement straight from the manufacturer for less (~140) than what Burley wanted (~200+ if I remember correctly).

I personally would recommend not spending alot on the trailer because likely your 6 year old is likely near the end of trailer riding days as he/she will be getting too large for any of the trailers I have seen. The 3 year old will likely start to transition out of the trailer ~5. Unless you plan on having more kids, you will have about 2 solid years of use for the trailer. Your 6 year old is getting stronger and could start contributing to the riding effort via a tandem, tag-along or single bike (for shorter rides). 6 is about the limit of when they will ride in the trailer for any amount of time. I think this is not only due to space constraints but also because of increased capabilities around that age. Of course special needs are a different issue and there are one or two trailer manufacturers that make trailers for special needs. My 6 year old will do short rides in the trailer but I can't do the multi hour rides anymore with that one.

I have ridden all 3 of my kids in the trailer, 20 + 35 + 45 with no problems. It was a tight fit but we did not go far. I have also ridden some older kids that thought it was cool that my kids were in the trailer. I think I probably had ~175lbs in the trailer. It looked like maybe it flexed a little bit but again, no problems on the short ride. I did get them to about 22mph, downhill of course .

One feature I wish the Cycletote had was reclining seats. I think the Trek model offers that. I also wish it had an indent for helmets so that their chins did not end up in their chests for when I do have them wear their helmets. I have found the major brands to have very similar inside dimensions.

The trailers weigh about 20-30 lbs. Add in the kids and you can easily reach 100lbs of extra weight. Pull that consistently for a awhile and you will get used to it. I am so used to it that not having the trailer on the bike makes my bike feel like a rocket that I cannot control the steering on. Very odd but pleasant.

Good Luck.