Orcs and Chaos are strong in leagues [I play Orcs myslef] if they get the right advances [as are dwarves but since they will never really be able to play a passing game it makes less impact later in a league lifetime]. No experience with Lizardmen but they look strong on paper.
The new generic Elf team looks like it could get some mileage.
Best team straight up though, Skaven. Absoulutely no arguement about it they're little bastards and will beat just about any team unless their coach i lame or the other team gets REALLY lucky.