I can see this tread turning to crap very soon.
Colour is a personal preference, there is no BEST colour, just peoples favorite colour.
Its like saying what is the best road to drive on, the best music to play, the best movie to watch, the best restaurant to go to, the best motorbike out there... You get the idea...
If you are gong to go to the trouble and expense of a re-spray, then DEFINITELY do not go for a stock colour...
But keep in mind that if you do go for a different colour to the colour you have now, you will not be able to get away with a cheap re-spray.
The car will need to be stripped of all the external fixtures and fittings, engine will need to be taken out of the engine bay, and the whole lot will need to be sanded back, prepped and re-sprayed. (Think engine bay, door sills, boot, and all those impossible to reach places will need to be prepped and painted.
If you are going to go for the same (or very similar colour), then you do not need to go this far. (I.E. its not going to look too bodgey if the shade of red in the engine bay doesnt quite match the shade of red on the car...)
This will reduce the costs of a re-spray quite significantly....
Hope this helps