I find Neef brushes the best. They are generously bristled and come to a fine point and retain their flexibility after use. They are also easily cleaned and spring back into shape very happily.
Without trying, I have somehow gravitated to round brushes for oil painting and am much happier painting with the round shape rather than flat brushes.
But I really think its the Neef brand I like because I also have the same feelings about their use for watercolour. For me they really "fit the Mitt"
Cheers
Helen