My favourite one at the moment is a free one on Sky news website. There have a few free things each day, 3 sudoku (easy medium hard), 3 mental arithmetic ones, and one called Make Tracks (which I find addictive).
I used to do sudoku years ago but I don't seem as good at it now. I did books of logic puzzles 40+ years ago too.
If you want pattern recognition then jigsaws are fun. You can turn them over if you like just looking at shapes and do them from the back. I've done it with 500 piece ones. I found the 1000 piece ones too easy so I had a 4000 or 5000 piece one once, but it was too big. It took ages to do as well. It was a proper challenge, but could be frustrating when you spend an hour and don't do 1 piece.
I think the issue is to find the right balance of reward and effort. Not too easy and not too hard.
