Over my touring life, I have used four different sets of panniers. All separate. Far easier to use mass transport systems if needed at beginning and end of trips, which I usually do. My first were a set of secondhand Karrimors.....tough and serviceable, and passed on to someone else when I bought a set of Ortlieb roll tops...even tougher and absolutely waterproof...used for many years but quite frustratingly lacking in extra pockets to store stuff you need easy access to. I still use these for my weekly shop.
I was seduced by the marketing of the very attractive Arkel range....however, although I think it's worth spending more on panniers that will see heavy use (which mine do) they were way out of my price range. I finally got a set for under half price on
eBay (still a fair sum). They had a whole range of extra pockets and additions in which to organise your belongings! Like suitcases for the bike really! However, I found them a bit too heavy in practice and ended up selling these on to someone else. Who loves them. Extremely well made, tough. Spare pannier fitting mechanisms available So easy to pack, organise and access gear. But not waterproof.
So back to the old Ortlieb top rollers for a while. Which kept getting borrowed as younger members of the family started going off on trips without me. So, seemed necessary to fork out for a new set....I finally settled on the Ortlieb Bikepackers. They do have a few little extra sections to stow stuff you may need quick access to. Fully waterproof. Seem fairly tough and serviceable. Extremely simple pannier connection points and came with replacement pannier fittings, so far not yet used. Love 'em. Not sure yet if they will stand up to as much rough treatment as the roll tops, which have been thrown down mountain sides and on to station platforms, crushed on trains, submerged in streams and rivers, but they have been left out all night in torrential rain (with gear inside remaining absolutely dry).
As to double or triple....double and separate every time for me, with bungees to strap extra kit to top of pannier rack as needed. (This last trip which I have just completed ( 3 and a half weeks in Scotland and Hebrides) I generally had the tent, poles and my new Helinox chair strapped to top of pannier. Plus food supplies when purchased. I find it a far more versatile arrangement.
I, too, would worry about cheaper options on tour. How tough are the fittings on the Aldi ones going to be at that price...I would just be worrying about them breaking every time I went over any rough terrain.
