You say HIGHEST QUALITY so I'm assuming you DON'T want a 400mah eGo spinner?
The 400mah eGo spinner is TINY. Its palmable and I love it with a little clearo on top.
If thats not for you... There are a lot of SMALL mods out there. Do you want variable voltage or not?
If you don't care about variable voltage, then there are a few small mods. Anything 18350 will do.
The 18350 battery is about HALF the size of a 18650 battery and most mods that take it are palmable.
For instance, the Smoktech Telescope can be used in 18350 mode and its seriously 1 of the smallest out there.
(that is also very easy to get at)
There is also the Super-T 18350 mod. Thats probably the highest quality all-mechanical palmable mod out there.
(that is very easy to purchase... you dont really need to WAIT for it. its on the site, just click check-out)
Super-T also makes a 10440 model that is pretty much the size of a cigarette.
While the batteries won't last very long in the 10440 model, if you cary around extras, which are the size of AAA,
you'll be able to change them out whenever you feel the voltage start to sag off.
The Legacy mini is another one of the smallest high quality mods that takes an 18350. Great little mod.
You can also buy replacement parts for it, including a larger tube if you'd like to use it as a bigger mod, or w/a kick.
Another mod to consider is the REO MINI.
The REO MINI is probably the SMALLEST mechanical (high quality) mod on the market in my opinion.
You get a teeny little 510 atomizer for it, plug it in. The juice stays in a bottle inside the Reo's body.
When your atomizer is getting dry, you just press the bottle, and juice goes up a tube to your atomizer.
This design, which is pretty much only obtainable in REO's mods, aka a "bottom feeder"
allows the reo mini to be one of, if not, probably THE MOST smallest mod on the market today.
The entire mod, including the juice delivery system, can be concealed in your palm pretty much.
Because the REO is bottom feeding, there is no need for long cartomizers, or big tanks.
the tiny, SHORT, atomizer, and a drip tip, is all you need, because the juice is fed from within the mod itself.

The Reo Mini is NOT variable voltage, but you can use it at 3.7v w/its 14500 bats, OR 6 volts with 2 14250 batteries
Another new mod on the market is the Smoktech Natural, which comes with an 18350 tube & an 18650 tube.