Based on my observations, about 95% of bicycle tourists opt to use panniers. There are good reasons for this. With two wheels on the pavement rather than four wheels, drag is cut in half. I have experienced this first hand on mountain descents. I was traveling with my two wheel trailer and had met up with another cyclist riding with very heavily laden front and rear panniers. Our total weight was similar. When we began our descent, side by side, neither of us pedaling, he quickly pulled away. The only explanation was the extra drag I was experiencing with two more tires on the pavement.
Panniers do have disadvantages, however. All that weight on the bicycle will make you think twice before going off saddle on hills. When you go off saddle, a bicycle tends to lean back and forth slightly as you pedal. The problem is that the panniers also start to lean back and forth. With all that weight in the panniers, this can lead to a loss of control. This is a big issue for me because I like to occasionally go off saddle on hills. It helps to work your muscles at a different angle. Also, if you are trying to raise your anaerobic threshold, nothing works you harder than going off saddle.
A less important issue is that you have to divide your load into a multitude of containers. Larger items like tents and sleeping bags tend to end up strapped on top of the rear rack where they are exposed to road filth when it rains (even if you have fenders). It is a lot of work just securing the load. Finally, even though touring bicycles are designed to handle the extra weight, I have encountered cyclists who had to contend with issues like broken rear spokes. These types of problems can cause a lot of stress. My love of vintage Italian road bikes from the seventies and eighties led me to consider a bicycle trailer rather than panniers since road bikes work perfectly well with trailers but lack the necessary fittings to accommodate racks for panniers.
Now, let’s consider the advantages and disadvantages of bicycle trailers. I have already mentioned the extra drag from having more wheels on the ground. You will also get more flats simply because you have more tires to contend with.
The primary advantage of a trailer, on the other hand, is that it takes most of the weight off the bicycle. A two wheel trailer will only put an extra 15 lbs. or so on the rear wheel of the bicycle, depending on how you distribute the weight in the trailer.
A one wheel trailer, like the Bob trailer for example, puts 50% of the total trailer weight on the rear wheel. This is because the single trailer wheel extends BEHIND the cargo deck, suspending the cargo between the single trailer wheel and the rear wheel of the bicycle. With a single wheel trailer you will also encounter the same weight shifting issues as panniers. Again, you won’t feel comfortable going off saddle when climbing.
The biggest advantage of a one wheel trailer, of course, is tracking. You don’t have to worry about dropping a wheel off the edge of the road or curbing the outside wheel. This was my biggest concern when I purchased a two wheel trailer. It turned out not to be a big deal. Your brain quickly adjusts to the extra width of the trailer without any conscious effort. (If your brain fails to adjust, the nearest curb will quickly remind you!)
The primary disadvantage of a one wheel trailer becomes apparent when you are trying to pull everything up a steep embankment or over rough ground to a camping spot. Even very tall grass can make it almost impossible to pull a trailer while it is attached to your bicycle. With a one wheel trailer, you can’t solve the problem by detaching the trailer. The trailer will just fall over to one side. A two wheel trailer, on the other hand, easily detaches and is easy to pull by hand up even very steep embankments. This was the decisive factor for me because I look for free spots to camp almost every night.
After considering all these factors, I believe you will either want to go with a touring bicycle and panniers or with a road bike and a two wheel trailer. I would make the final decision based on weight. If all your gear weighs 40 lbs or less, go with panniers. Over 40 lbs, go with a two wheel trailer.
Your total weight is likely to be determined by the groceries, cooking fuel, and water that you are carrying. I cook three meals a day, carry water for drinking, cooking, and bathing, carry all the tools necessary to completely disassemble my bicycle, and carry winter clothing items. Thus, it was pretty obvious that I needed a high quality, two wheel trailer.
On one trip, I met a young couple who were also on a long bicycle tour. The husband was using front and rear panniers. The wife was pulling a one wheel trailer and traveled behind her husband. I was surprised by this arrangement because I thought the wife had the harder task. I asked them about their travel arrangements. Their answer surprised me and proved that there was at least one characteristic of bicycle trailers that I had overlooked. The wife explained that if her husband pulled the trailer, the trailer would prevent her from drafting close behind her husband, who was the stronger rider. By pulling the trailer herself, she could position herself very close to her husband’s rear wheel for efficient drafting.