preferred fan speed control methods?

[Drew Van Zandt]

A comment on Dave's question about fans blowing in vs. out:

Air at lower pressure than "normal" can have really weird flow
patterns and utterly fail at cooling parts of the inside of the case.
Air at higher pressure is fine.  Push air, don't pull it.

Also, if you're filtering as the air is coming out, you're not doing
any good for the inside of the case, just for your air.  Filter before
it goes in, less dust gets on the fan blades and internals.
Higher-pressure air inside also helps keep dust from sneaking in the
crack, as there's airflow out through even the tiniest ones.

--DTVZ