One of the good things about titanium is that it's used for fancy, speciallized gear. It's expensive, so it gets used in small, lightweight designs. There are lots of big aluminum or steel pots out there, and lots of truly tiny titanium pots, but very little crossover. So you save weight by carrying something smaller, and more in line with what you actually need.
While aluminum is lighter, it is also weaker. Titanium is a bit stronger and heavier, but much less so than steel. There are all sorts of material-property numbers to throw around, but it's still difficult to tell what would work best, especially in something so simple as a pot. I'd guess that thin aluminum would be the lightest, but would dent easily unless you took very good care of it (then again, that's true for most superlight gear).
I switched from a 2 quart MSR stainless steel pot to a .9 L Evernew titanium pot. Advantages of the Evernew - perfect size for solo cooking - with a maragin of error for liquid slop and could serve 2 if needed, nonstick coating is pretty good, and makes cleanup much easier; integral handle means you won't lose the little lid lifter gadget. Minuses - the silicon coating on the handles (a plus because it keeps things cool enough to touch) singe in flame. I use it on a Trangia alcohol stove, which is very small and fits nicely inside. The alcohol is prone to flare-ups or crawling up the outside of the pot in strong winds.
Were I buying now, I'd also consider the MSR Titan tea kettle, but it would be hard to give up the nonstick coating and silicon handle coating. REI carries all this stuff, with a somewhat limited selection of Snowpeak items. Also having a sale - 20% off one item for members - that ends Sunday the 15th.
