[Arran]

Well the 18B only has a broadcast and a police band, like a Philco 60, but then again it has push-pull triode connected 42s driven by another 42, also a shadow meter, so it's a real thumper for audio. The 44B has four bands, like a 16B, but only has six tubes and a single ended power output stage. If you like raw audio power go for the 18B, if you like DXing, go for the 44B. I don't think that one is worth any more then the other, but the 44B is likely a rarer set.
Regards
Arran