What is more important to have in an oil filter, an anti-drainback valve or synthetic media?

I'm trying to decide between these two oil filters:

PF35L - PF35 with synthetic media
PF1218 - PF35 with anti-drainback valve

I've heard the PF35L filters to about 12 microns while the 1218 filters only to 30 microns. I've also heard that an ADBV is unnecessary for engines with oil filters at the bottom (supposedly gravity works as a "natural" ADBV).

Anyone care to shed some light on this?

Laws of physics would dictate that, barring any reversal of gravity or a change in the gravity vector (ie. flipping your car onto its top), the oil would not be able to flow up and out of the filter on a typical SBC motor found in our cars.

I've got a shelf full of PF25s, all of which have no drainback valve. The few 1218s I have do indeed have the valve, but it is unnecessary on Gen I Chevrolet V-8s. The 35L is a good bargain on a polyester medium filter, and if you have the clearance under the car, a good choice.

I had pretty much made up my mind to go with the PF35L anyway... I just needed the little extra "push" to go for it. Thanks.

Is that the huge 1 quart delco filter?

I don't believe they make the PF35L anymore though.