During the past years I have tried lots of different brush brands and there seems to be huge variety even within a single manufacturer. I still use my eight years old Citadel basecoat brush while I have been wearing down many Citadel detail brushes. Pro Arte brushes have been very durable and good quality for their price and they even have a special range designed for miniature painting.
Now I'm test driving Winsor & Newton Cotman series and they have been so far wonderful. They keep their tip sharp, hold paint inside them very well and deliver it consistently. I ordered them from ArtiFolk for the price of about £3 per brush.
A very important thing to do when looking after your brushes is to make sure you don't dip the brush too deep. Keep the paint far away from the 'roots' or the metal ferrule between the bristles and the handle. It's a pain to clean up and any dried paint there will make the individual bristles point at various directions, which, well, is not good.
I usually rinse my brushes before getting more paint from the palette, so that's every few strokes, I guess.
-- Pasi