If it's only going on road I've used all sorts over the years and not noticed any difference. Halfords own to motul race stuff, the biggest issue I've had is bleeding them afterwards.
I use this . ATE Super Blue Racing Brake Fluid DOT 4 - 1 Litre | eBay . If you are changing it totally its good to have a different colour as you then know when it is through .
+1 on the ATE super blue fluid (alternate with normal, I just use Pagid fluid also from ECP) Euro car parts seem to be the cheapest (inc p&p) ATE Super R Blue Dot 4 Brake Fluid - 1 Litre
Apart from the fact that it is pretty well colourless, this appears to be an even better deal. It's what I use anyway: Shell DOT 5.1 High Performance Brake Fluid Car / Bike - 1 litre ltr | eBay Smith & Allan - generally very good deals on Shell lunricants etc. I think they do DOT 4 as well, but my understanding is that it's only DOT 5 that should be avoided, with DOT 5.1 being compatible with 4, simply slightly higher boiling point etc.
Some dot 4 fluids have a higher boiling point than some dot 5.1 fluids . Its a minimum boiling point that the Department Of Transport have set out dot 5.1 being 190c and dot 4 155c . Good fluids can have a much higher boiling point than poorer fluids . Therefore you can have a dot 4 with 200c + and a dot 5.1 with 190c . Dot 3/4 or 5.1 can be mixed but not with dot 5 . More use (less) information .
