I think a big piece of Sunrise's best and brightest ended up at BONES, and then a piece of their most interesting people then ended up at Manglobe.
In terms of an overall track record, a lot of studios can have good cases made for them and against them. Just as Sunrise, BONES, Manglobe, Madhouse, Gainax, Production IG and so on have made some very good shows at a fairly regular clip, they've also made some total throwaways too. Some of might average out a bit better, and there is certainly evidence that at the feature film level, studios like Gainax, Production IG, Bones and Madhouse (especially Madhouse,) are able to do work at a level that a lot of their contemporaries just can't touch, but everyone has their D-titles.
Edit: Ghibli over their history maybe has the best hit to miss ratio, so while it's entirely unfair to put an art-driven studio that never has to worry about feeding itself against the commercial studios, I shall say Ghibli is the best anime studio in Japan.