This is probably the only useful Samoan/English - English/Samoan Dictionary available and in print.
I have heard of but never come across a copy of Pratt's and Parker's Dictionaries. There is also a French-English-Samoan Dictionary dating from the 1800's. I found a copy once on the Gutenberg Project but if you can find an actual copy it would most likely be the the rare books section of any library that has it. Papalii's 2 volume set is not a proper bilingual dictionary and I'd advise anyone not to waste their money on either volume.
That leaves Milner which really needs to be expanded and updated. Until then it is the best available.