Well, they'll will both do the job fine. The Nilfisk one comes with the patio cleaning kit so has everything you'll need for £70.
The Aldi one you need to buy the patio cleaner separate for £25 (which they also have in store)
The Aldi one is slightly more powerful in pressure and flow and has a longer hose, a storage reel for the hose and a longer warranty.
The Nilfisk is well regarded (a lot say better than Karcher) and is easy to get accessories for (snow foam lance etc...) Although I'm sure you could get one to fit the Aldi one easy enough.
Your decision mate. I went for the Aldi one for the reasons I said above, but I doubt you'll be disappointed with either.
Cheers mate, just ordered the Nilfisk one. I borrowed my brother in laws Karacher last year and it had the patio cleaner and was awesome.
Good excuse to buy a snow foam attachment now, lol.