I don't care for CBS's interface at all; it's content is very much superior to Yahoo's and the tools at your disposal are excellent.. but for sheer ease of use and user friendliness, SportsLine blows.
One of my favorite features in Yahoo is sorting players by their ranks; the Yahoo Rank, the overall fantasy rank for the year and also their ranks in the last week or month. I use this is extensive in Yahoo to keep track of which players are more consistent than others. I know there are ways to do this on my own, but I just find the simplicity of Yahoo's interface superior over SportsLines.
StatTracker is also much, much better than Sportline's GameCenter, which is extremly buggy and difficult to read with all the commas everywhere.
I also hate that the per-game stats are not "easily accessible." Maybe I sound like a whiney newb, but the baseball season is long and sometimes all I can give is a quick glance in the morning.
Overall, I don't think I'll be using CBS again.
If you're a battery, you're either working or you're dead....