I reckon you can enjoy riding more with a decent set of panniers. You do feel the weight on the back but you can still do just about everything with them. A trailer makes you longer and you always have to think about the extra length. I reckon it might add more drag too with an extra wheel, but I’ve no evidence for that 🙂
I’d always choose panniers unless I had too much weight.
I’m planning a bike/train trip with the family – train to seaside, cycle 10 miles to campsite, camp for a week – which will see me carrying all the gear and two kids in panniers and trailer by way of handicap. It’ll be fun 🙂