What is the smallest particle

What is the very smallest sub-atomic particle?

I am unsure on this but I have read that quarks inside a proton or neutron are the smallest known particles. As I understand it, quarks and electrons are currently considered to be fundamental and indivisible, the smallest of particles with the quark being tinier than the electron. It is after all, three quarks exchanging mesons that gives protons (2 up-quarks and a down quark) and neutrons (2 down-quarks and a up quark) their intrinsic
shape and characteristics.

See: Electron vs Quark Size
http://www.newton.dep.anl.gov/askasci/ph…

See also: Structure of Matter
http://sciencepark.etacude.com/particle/…

Nucleus = about 1.0 x 10^(-14) m
Proton = about 1.0 x 10^(-15) m
Electron = about 1.0 x 10^(-18) m
Quark = about 1.0 x 10^(-20) m

I have heard it described by one physics professor as three quarks inside a proton is like three galaxies inside the whole otherwise empty universe.

In term's of mass it is "Electron Neutrino" which is a subatomic lepton elementary particle.

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The hydrogen is the smallest atom so there for the electron of the hydrogen is the smallest.