During my last cycle trips around Europe, South America and North America, I used my bike with a trailer. The trailer really fascinated me, largely due to the fact that the one wheel trailer is great on tar roads as well as on dirt roads and it is much easier and faster to pack - just throw everything in the big 90 litre waterproof bag and off you go! Now, I use 4 large panniers and a bag on the back rack with my new Tout Terrain touring bike. I find, both ways of packing has advantages as well as disadvantages.
I have carried out a number of tours, both in wet and dry climates which has helped me choose the correct equipment. BUT: Equipment can never be perfect - an Ortlieb waterproof bag is great but a squirrel can easily bite a hole through it and steal the peanuts inside!!!