X2 - the plate type is better as to heat rejection (needs less total cooler, and less surface core presented to the atmosphere), but I suspect the internal shape allows a bubble to become "flat" and just refuse to change back to round to get back out.
You can just break the line at the exit to get any air out after initial start, but a bubble caused by uncovered the pickup or aeration is harder to purge.
I've read that an infra-red gun can tell you if there an air-lock problem because the plates will show different temps (the upper plates will be cooler since no oil passes through), but I haven't done it.
