ANY good non-oily solvent will be good. Some will be better that others. I'd recommend against nail polish remover, because of the aromatic oils included...
Acetone, isoproponal, ether, all would be good.
The difference between the various percentages of isopropanol is the included amounts of water... So the drying times vary. Not by much...
Ether, acetone, lacquer thinner and isoproponal are all very hygroscopic. (This means that they absorb water....) So as soon as you crack the seal on a very high percentage, it will start absorbing water.
I can remember a thread a while ago where someone used peanut butter as a HS compound, quite effecively.
On the other hand, Wusy will hand lap his hitsinks and the top of the CPU to a high polish prior to applying paste.
Whatever works, guys, for you. Just get it clean, preferably dry, prior to applying your compound. If you use something with oils, (I've heard of lighter fluid being used) then try to remove the oil first. Isopropanol, water, and a dot of detergent, followed by some drier isopropanol to clean up the mess...
On another note, isoproponal at 50% is recommended by most LCD manufatcurers for screen cleaning...
I use 70% isopropanol, and patiently wait for the 60 to 90 seconds to dry. Works for me.