Both are decent filters. This subject has been beaten to death on more than one forum site.
Some swear by AC's while others the Emp.
I have kept AC's for longer than I can remeber, and some of those are still running!
I never tried the Emp's but why change a good thing and something that I know and trust to work? I have had some exprience with the Pengiun 330.
So my vote goes to the AC. The larger intake and the larger motor makes the AC110/500 out shine the others in the line. The 300/70 has the same size intake but has the smaller motor, or atleast it used to be that way I havent owned on in 6 years or so.