It is a hard question,
we can only answer what
we'd choose. Ortliebs are quite a big investment and then last decades, I can't remember when I bought mine, I have a photo of using them on a tour in 2007 and think I'd already had them a couple of years, they're still in daily use and look in decent condition. These are the heavier classic style, I'm a bit dubious about the lighter material used for the Plus versions, though have no experience.
If I'm touring for more than a few days I'll be camping and for shorter trips a saddle bag suits me fine. I have done the full goldilocks routine, Too much>Too little>Just right and even then it's still under constant revision. Even camping I find two smaller Ortlieg panniers (30L) a bar bag and a saddlebag (9L) is sufficient, I subscribe to Moronic's theory, which works for me in practice, the saddlebag and bar bag contain what I'd be carrying on a long day ride, with some capacity left for shopping. I rarely have need to open the panniers from one end of the ride to the other.
In theory having two smaller bags and a rack pack allows you to put your overnight stuff in the panniers and save the rack pack for things that you might need more often.
That just leaves the panniers, one is entirely camping kit (Not including the tent which is outside), leaving everything else is in one (15L) pannier. I'm fine with that, though it doesn't include extra footwear (I use flat pedals so don't need special cycling shoes), I'll also choose cycling kit that doesn't look too out of place off the bike, and I have no need for passed shorts so don't have that bulk. Summer cycling in warm climates allows you to wash kit in the evening and wear it the next day, I can do that camping so it'll be easier staying in accommodation.
But this is no help to you! You may find daily laundry a chore, like plenty of cycling kit, dress for dinner... There's no right and wrong, the only advice I have is that you're unlikely to get it right first time. Panniers are just bags that fit on a bike, Ortliebs or Aldi, they're not going to make or break a trip, I'd be tempted to buy cheap big ones, maybe secondhand and use a bit of trial and error, to see what works for you.
Well, one other bit of advice, get a neutral colour, you may find over the life of a pair of Ortliebs they'll be on several bike, you don't want them clashing!
EDIT - A not very good photo to illustrate the above points. The last longer non camping trip I did, 2004, half way through an 1,100 mile, 11 day E2E.
My bike on the left, an under saddle tool bag, bar bag and a pair of Orlieb panniers that have been cut down to about 22L the pair (To fit a small wheeled bike) My companions bike on the right, same bar bag and similar saddle bag, plus huge 45L panniers, crammed full.
It was a source of amusement to us both how much/little the other was carrying, but neither of us would have made any significant changes were we to do it again.
Falstone by
Paul, on Flickr