High viz or cool?

Lights are your best bet. Buy the best you can afford and use them, especially a flashing front, even in daytime. Constant lights and flouro jackets can be lost against a busy background especially if you are static relative to the background, as is the case when a driver is pulling out and looking left/right.
I use one of these front:http://www.jejamescycles.co.uk/use-exposure-joystick-item120038.html
And one of these rear: http://images.google.co.uk/imgres?imgurl=http://www.dotbike.com/A_Resources/ProductImages004/P4140_125.jpg&imgrefurl=http://www.dotbike.com/blt.aspx&usg=__EXCVzeWDXLrpqtY4-2Hb7we6cSU=&h=125&w=125&sz=5&hl=en&start=1&um=1&tbnid=NqelkFfN7K8pVM:&tbnh=90&tbnw=90&prev=/images%3Fq%3Dblt%2Bfantom%2Bx9%26hl%3Den%26safe%3Doff%26sa%3DN%26um%3D1

But whatever you choose remember: Drivers will fail to see you, but: All drivers that have seen you are a out to kill you. Especially bus and taxi drivers.

Be safe.

Good advice.

+1