HSV = 3,600,000 values
(photoshop) Lab = 6,553,600 values
RGB = 16,777,216 values
CYMK = 100,000,000 values
Hex = 2,176,782,336 values
32bit colour = 4,294,967,296 values (?)
its the truth. however CYMK on photoshop is limited to the number of colours possible with the RGB values.
if we wanted all the colours possible on a 32bit screen we'd have to have RGB values from 0 to 1624 i think.
anyway the point of all this is that Hex = 'smoothest' in terms of number of possible values. however its hard to colour with just hex values to go on. so do whatever you find easiest i say. and HSV looks smooth enough. the human eye can't really tell the difference better 254,254,254 and 255,255,255 can it?
erg just realised lots of these numbers aren't correct. some you won't get any values if one of the numbers is 0 so i think only RGB and Hex are accurate. all others show less colours then stated.
CMYK = < 65536 colors (it's a print-oriented colorspace, after all. And ya'd be lucky to get 16 different sizes of ink blob supported by the printer.. probably it's closer to <4096. (8^4)
Hex = Infinite .Hex isn't a colorspace. while photoshop etc display these hex values like RRGGBBAA, their actual range and number of bits depends on display hardware. for a 32bit hex number, there are 4,294,967,296 values; for the more common 24bit hex value, 16,777,216; for the 48bit format used by X11, 281,474,976,710,656 colors (normally not used for display, only for high-precision manipulation). For 16bit displays, there are of course 65536 colors, or 32768 for 15bit (I favor 15bit).
HSV is also fractionally adjustable, as is RGB, depending on your paint program. That finally means it provides (more than) all the possible displayable colors. On modern machines, this may have up to 80bits of precision (GIMP is a known example), which amounts to 604,462,909,807,314,587,353,088 unique values. (79 ^2; 80 - (1 bit to store the sign))
The human eye (at least my human eye) can tell the difference between 254,254,254 and 255,255,255 if they are the only two colors onscreen.
This is all beside the point though -- 64k colors should be enough for anyone!