Hi,
I've tried over a dozen LW receivers from the DX[xxx] series from Radio Shack tohomebrew to the Grundig's and now have an Eton E5. With a decent antenna (like a nice big loop), it really doesn't matter sensitivity wise, it's selectivity you want there.
Fortunately, any good SSB with a narrow IF filter will do wonders, because the aero/marine NDP's are really loose tolerance on the 400Hz (Canuck) or 1KHz (US/most of the world) tone and you can zero-beat most unwanted ones in a pileup.
Fow longwave sensitivity of eveything I tried, the old DX200 won hands down. But being a simple circuit, overload, AM interference and selectivity sucked bigtime. I had to make a 9-pole LPF just to keep the AM out on that one.
The worst was the DX300/302. Specs are a complete lie... I lived right beside a military base and had volts per metre of CKN on 133KHz floating through the house.... if I made a renonant loop, I could light a small flourescent bulb in it. Pfffft! S-8 on the DX30x? C'mon!!!! Overload/IF was pretty good though - CKN didn't swamp it where a Satellit 800 was frackin' useless and had to be returned.
Unless you go to one of the ollllld rigs specifically designed for military coms or a LF AC voltmeter (those are great) on Ebay, I'd check any little portable and concentrate on antenna, antenna, antenna.
My twonie....
Peace!