I use a mixture of two different brands.
For basecoats, drybrushing and general painting I prefer ProArte's Miniature Painting Brushes, size 0 or 00. They're fairly cheap and last forever in near-perfect condition (last one I bought was £1.50 and has lasted me almost four years now). I believe they are difficult to come across, although I haven't looked online, but when I've popped into various art and hobby shops throughout my region (South East of England) I've only ever seen them in one shop which has since closed down, so I'll need to look online for replacements from now on.
For detailed work, edge-highlighting, freehand, etc., I devote myself to the Winsor & Newton 'Cotman' range for watercolour painting. If you look after them, following the basics of brushcare, then they remain in literally perfect condition - the three I use are all size 00 and have lasted nearly six years now, they still look brand new aside from staining on the wooden stem. I have also used size 000, but found that they were much less durable - I barely used this size but when I have the brush only lasts about a year before the bristles begin to buckle or disintegrate, despite caring for them in exactly the same way as my size 00s. Since about 2012 I've relied solely on size 00s from the Winsor & Newton 'Cotman' range. From memory, I payed something like £3 for each brush, but like I said, they last for an eternity so it's worth it.
Finally, it's always good to have a 'crappy' brush lying around for basing, drybrushing large areas, or general wear-and-tear that would destroy good quality brushes in an instance. I use Winsor & Newton's student quality 'Fine' range. In my local hobby shop I get six brushes in a pack, (sizes 1 x2, 2 x2, 3 and 4), and this costs about £5. They don't last long in perfect condition, but that's because I don't look after them. But they do the job I need them to do, slapping sand and PVA glue onto bases, or drybrushing frantically. They're bound to get damaged for this purpose.
I've got a decade and more's hobby experience so I've had my fair share of brush calamities and successes. Hope this helps.