block heater question - getting ready for the winter early...........

[millertyme]

i know that this question is at the wrong end of the season, but i am
planning on changing the coolant and thermostat this summer and want to
get everything done at once.
the question is, what form of engine warming is used by fellow listers?
i am debating between the in-line heater and the block heater (frost
plug).
does anyone care to share their pros/cons to either or both?
thanks
brian