If you want to barch for league bonus, crystal 2-3 are best. I also newly upgraded to th 10 and barching league bonuses can keep my builders busy. Not too much challenge of course, but no point in going to master leagues if you'll get flattened the second you're logging out. Especially as th 10 hold the most loot and no one get penalty attacking it.
Another thing I've been trying to do this season is to stay at gold 1 and use balloonions vs th 9s. Need longer searches, but can get good loot as th 9s like to stay around this league for some reason.
Overall, I think going on lower leagues is a better bet for this season. Everyone's became very active last season and the constant raid vs each others have pushed the lower town halls and inactives down.
