I have used two different one wheel trailers over the years. This past spring I started using a two wheel cargo trailer. The comparison of the two types of trailers has led me to some experience with their relative benefits that I think could be helpful to other people wondering about bicycle trailer choices.
Before I built my Cadillac El Gordo commuter bike, I had quite a bit of success with two brands of trailers that have one wheel and are of similar design:
The Bob Ibex and the Nashbar Cargo trailer. The Bob trailer is much more durable at about the same weight as the Nashbar trailer. The Bob trailer is much more expensive than either of the other two trailers listed here, but if one can afford it, it is well worth the extra expense. The Nashbar trailer that I have was built several years ago. Nashbar says in their catalog that the current version of this trailer has been upgraded with a stronger construction. My Nashbar trailer frame bent early on, but I reinforced it and had reasonable use after that, being careful to keep the loads at less than 35 pounds. The Bob trailer can easily carry loads at twice that weight, but I don't usually want to pull more than about 45 pounds as a practical and manageable load for me.
The Nuvinci 171 internal gear hub on my bike has a non-typical axel nut configuration that prevented me from using either of the one wheel trailers I already had. These one wheel trailers mount on the bike by replacing the quick release skewer with a skewer that also mounts the trailer. I could not make either of those systems work on the Nuvinci axel, so I found the Croozer Cargo trailer with a trailer hanger that mounts asymmetrically with an attachment that is held on by the left side axel nut. This works well with the Nuvinci hub.
So, my Nuvinci Bike uses the two wheel Croozer Cargo trailer. I also have added a
The Trailer Advantage:
All three trailers are a huge improvement for carrying anything that is too bulky or too heavy to fit easily in my standard behind-the-seat rack carrier. The trailer lets the bike feel like a bike. A trailer puts less strain on the bike wheels and spokes. Panniers and other rack mounted carriers, in my experience, put more side loading forces and non sprung weight loads on the wheels. Panniers make the bike feel cumbersome and sluggish. Trying to ride with a big pack on one's back is the least desirable and most uncomfortable of the weight hauling strategies.
Two Wheel trailer advantage:
For ease of parking anywhere, and for loading the trailer, the two wheel trailer combined with having the double leg kickstand on the bike is very convenient. For very simple convenience in town and a slightly larger volume capacity, the two wheel trailer is easy to live with, But....
One Wheel Trailer Advantage:
Once I am actually moving, I really, really prefer the one wheel trailers. Either of the one wheel trailers seem to pull easier than the two wheel trailer, they track and balance naturally, and I never have to worry about where the trailer wheel is going to track, and it is always in line with my front wheel in a totally predictable way.
The Bob trailer and the Nashbar trailer also keep the load slightly lower.
For all these safety reasons, my ideal trailer would be the Bob one wheel trailer with the addition of some type of trailer kickstand to make it easier to park and to load. In town, one can usually find a wall, fence, post, or curb that will balance everything, but when I am out on trails loading camping gear or tools, the one wheel trailer gets awkward every time I stop. That said, when using a two wheel trailer on these outings there is often just a single track of effective space for the bike wheels, so the two wheel trailer is always an annoyance and potential problem. The wider wheelbase means one of the three wheel tracks is always on a more resistant surface and hitting extra obstacles.
On rough roads with significant side slope or uneven road surface, the two wheel trailer is actually more unstable because the trailer tilts with the side slope of the road feature, while a one wheel trailer can stay exactly balanced with the bike.
Since I already had several years of practical experience with the one wheel trailer, I was surprised to discover how often the two wheel trailer causes safety concerns for me in town. The two wheel trailer forces me more than a foot farther out into the traffic stream than I sometimes would normally travel because I really have to make sure the wheel does not go off the pavement edge or into road edge grates and curbs. Also, the tracking of the wider wheelbase often gets caught if I am not extra careful about bike path gates, poles, or drainage features. Tight maneuvering and sharp turns exaggerate this problem.
For all these reasons, I highly recommend the Bob Cargo Trailer.