I prefer playing against unknown players . I started accepting "Smart Matches" and now many of those people have become my regular playing opponents (although they are strangers).
I'm impressed at how much I must learnt since I started playing in that my average word score has gone up. I've become smarter at how I place tiles e.g. alongside a word vertically and so on.
I also played "against the 'puter" recently, some or other Christmas challenge, which was fun, it got progressively more difficult e.g. the first level against the "Elf" was "Easy" and so on. With these wins, I have gathered points that permit me to swop tiles without missing a turn.
It is addictive, I have to hide the phone and play surreptitiously when I am supposed to be enjoying shared TV viewing ...