The best answer may depend on your field of study. My answer may be
biased because I am most familiar with the mathematical sciences
(including applications and statistics). Also, I'm assuming you're a
US citizen and both positions are in the US.
Especially if 'PhD candidate' is a euphemism for 'still working on my thesis', then
take the post-doc job, finish your thesis, and try to use the post doc
environment to get ideas for good starts on a couple of publications.
That extra experience and record of accomplishments will put you in
a strong position to get hired for a tenure track position and to
get tenure (in amongst dealing with class preparations and advising
students). If you start the tenure track position with finishing part of your
thesis still hanging over you, your chances of getting tenure may seriously
reduced. (Almost no university departments will grant tenure to someone
who is still working on a thesis and with no publications.)
I made the mistake of taking a tenure track position when my Ph.D. thesis
was "not quite finished". The environment there was not quite as promised,
the teaching load way high, and after one year it was clear that the
thesis was just as far off as before. 'Wasted year' would be putting it gently.
Then, I was fortunate enough
to be able to transition to a post doc at a major university during
my second year. There I learned most of the applied skills I have used
in my 40-some years since. Also, I made contacts that turned out to
be of amazing benefit as my career progressed. After the post doc I
took a tenure track job I have enjoyed enormously until my recent retirement in my 80's
(interrupted only by a few years working for the Federal government on
leaves of absence).