Challenges are fine if you happen to be good enough to play them and win (at least as much as you lose). However for the average golfers out there, including me, who want to play a round without someone quitting they are probably too expensive. There must be another way.
At this stage, for me, the most satisfactory is the ladders group. I can't speak for the other sites that offer similar experiences. I do occasionally try for a random game with some strangers but find that 90% of the time I have to finish the round by myself.
To date I've never quit a game voluntarily, even if my playing really sucks. I've put up with slow play from others and even total silence. I'm quite happy to play with very new players and find it rewarding to be able to give them some tips and help.
Cheers
Gregg