Tin foil is a horrible reflector. If you don´t have specially shaped reflectors, white paint is the best.
What do you mean by 'white'? The scientific definition of 'white' is that it reflects all colors. I do not know of anything that is 'white', even the most 'white' white paint that you can think of is not 'white'. Also keep in mind that 'white' paint diffuses the light---that is, it gets scattered in all directions.
If we are concerned about the color of our fluorescent lights, then we should also be concerned about the color of our 'white' reflectors. With our 6500K to 10000K lamps, this could be very significant. You could actually be hurting the situation by using 'white'.
'Tin foil' (actually aluminum) is an excellent reflector at all electromagnetic frequencies up to Xray. As far as the wrinkles are concerned, unless you are building an optical telescope, they are probably insignificant, IMHO. (telescope mirrors, by the way, are usually aluminum on a glass surface.)
What is important for getting the best distribution of light, however, is the general shape of the reflector and, given the same shape, a bare aluminum reflector will reflect more light than one that is painted 'white'.
Ok, now how many toes did I step on?