I have three baseball teams this year: two in Yahoo and one in Fox. The latter league is using Fox because the commissioner works for a subsidiary of Fox.
The Yahoo leagues have been great. StatTracker is a must-buy, but even without it, they've got some really nice features. One is for roto leagues: they show you a bar-graph-type thing that shows your team, the scores in that category for the teams on either side of you, and bars for each other team in the league. Very, very cool.
Fox, on the other hand, is crap. Some days it shows the wrong schedule: for example, on Friday morning, it would still show Thursday's games and tell you that you were trying to edit a future roster. You can't see the entire set of roto categories at once: instead, you have to scroll through them. They've had scoring problems all year and are still trying to work them out.
Today, it's locked all of my players, so I can't pull injured and bad ones out of the lineup to play better players. Apparently they're "locked for this week." I guess it doesn't matter that we lock players 5 minutes prior to game time.
If this were a random league, I'd quit and never return. (Well, it's also a money league.) Seriously. I don't know why Fox would bother with such a crappy setup when there are so many other companies out there who do it so much better.