I have a Stormy Monday with alnico IV in the neck and a Riff Raff with alnico V in the bridge, this gets a great tone, together they give that old Peter Green sound.
The Mule is excellent too, I have that in the neck with an Emerald in the bridge, but it is a bit more rocky with the Emerald, not that you can't get the great LP sounds with this, just a little more Thin Lizzy than Free! Tim's goldtop with Mules sounds great as well, Mules are the classic LP sound, but Stormy Mondays sound good too.
Another combination that I have which gives the old Carlos Santana sound (Black Magic Woman era), is a calibrated set of VHII's. This is in a PRS.
Backing off the tone and volume on all BKP Humbekers cleans them up for blues anyway - even the Miracle Man (when it has the alnico V magnet).
The only one I haven't heard is the Black Dog, Tim says that this is a lot of mids, so it might not be quite what you want. I am thinking of one for the bridge with an alnco IV VHII in the neck, but for more of Zep sound than an earlier blues tone.
Lots of choices, but they all sound great :)