There is no correct answer to your question.
At times I use both pannier AND a BOB trailer.
I carry an awful lot of stuff on my bike. Clothing, food, books, trip log, camera, stove, shovel, LOTS of water (three 28 oz bottles, 1 50 ounce bottle and a 10 liter MSR water bag).
I also carry a three/four person tent, sleeping bag, air mattress etc.
I use the ARKEL panniers. I wear a large butt bag and a large handle bar bag.
I carry two spare tubes, tools, spokes, pump, high pressure air cartridges. My tubes are slime filled and I have tire liners.
I also carry water purification equipment.
This is just a partial listing of what I carry.
I use the BOB when I travel somewhere and I take my camera equipment along. This I put in the BOB.
Otherwise, I prefer a self contained unit. This is the bike and the panniers.
I like the panniers for a number of reasons.
1. Easily loaded on an AMTRAK train.
2. Fits easily in the back of my airplane
3. I have everything I have found I need and it is in its own place (the ARKEL panniers have lots of storage areas).
4. Easy to remove at any time.
BAD points of my panniers:
1. My bike is really heavy - especially when I am riding in the summer and have loaded up on water. Note: I have found that three gallons of water a day is not enough for me when I am riding in the hot summer.
2. Often I don't use everything I carry. However, when I need it, I should have it available. On trips in the fall or spring, I just keep the 10L MSR bag folded up until supper time, then I fill it to prepare our meals.
3. The bike wobbles a bit, especially at speeds above 20 MPH. This is corrected by making sure that the panniers are connected properly. However, when I have the 10L MSR bag full, the bike wobbles more because the weight is on top of everything else I have connected to the rear rack.
4. If you use panniers, it helps to have BOTH front and back racks. This helps balance the load. It also means that you have to have four panniers and two racks.
My bike has front suspension. I use the Old Man Mountain front rack. This connects to the front axle and the V-brake mounts. It is a very sturdy front rack.
I use a JANDD rear rack. It gives my big feet room, so I don't kick my rear panniers.
Either panniers or trailer, you will enjoy the travels.
THere is no wrong choice (unless you buy the least expensive panniers, trailers, racks.