Totally agree with Redzed but I still buy Rosemary brushes.
W&N'S will always remain my favourites and I'll probably keep on using them till I can't hold a brush anymore. Should be any day now.

Still, the Rosemary's are good value for money and well suited for anything but the most precise work. You have to get used to the softer 'snap' though. Also keep in mind that the brush sizes between W&N and Rosemary aren't corresponding exactly
Has anyone tried the series 22 yet? Very handy for those hard to reach spots.
The Shiraz brushes are a godsend for drybrushing BTW.
I have been able to keep most 1s, Os and some 2/0 W&Ns for well over 5 years, but I clean all my brushes thoroughly after each session. Still remarkable if you know that I use oil paint almost exclusively and that Kolinsky bristles aren't exactly suited for oil paint.
Clean with purified linseed oil until no more paint comes off, then brush soap, shape them back and they (almost) last forever.
Odd thing: My wife uses W&N series 7
Miniature and these wear out much faster.