LIKE: THREE-PLAYER GROUPS
For me, three players is the sweet spot. With three players, everyone will get a large share of spotlight time. They'll get to play the game their way. They'll get to tell more of their story.
Also, in a three-player game, everyone is important. Each character will have a lot to do (assuming 1 character/player), since there aren't a lot of other people they can turn to for support. At the same time, it's not hard to challenge a three-player group, since they probably can't cover all the necessary bases every session. They'll have to improvise, generalize, and/or turn to NPCs for assistance. Everyone gets to be a lot more resourceful in a three-player game. I enjoy that from both sides of the screen.
DISLIKE: THE WEEKLY GAME
This one puts me pretty solidly outside the mainstream, I know. But as they say in Lake Wobegon, sumus quod sumus - we are who we are. And I'm someone who doesn't enjoy it when my roleplaying is an appointment. As a GM, I can't guarantee that I'll have a good idea every week. More likely, I'll just get burned out by the pressure of prepping that much material. As a player, I can't guarantee that I'll show up that often. This isn't a new development - even before I was an old person with job and spouse and kids, I rarely committed to a recurring game.
Scheduling your roleplaying that rigorously, to me, takes some of the fun out of it. Now it's not something we do because we're in the mood - we do it because it's an obligation. We have to play, whether we feel like it or not. I'd rather only play when I feel like it. And it's rare that I'll want to play once a week.
I did run a weekly game for about a year. It was a good time, too. That was entirely because of the people I played with - close friends all, and we knew that this was a limited opportunity because of jobs and weddings and stuff. If we tried to make it a permanent thing, I think we'd have driven each other crazy.