What are the best ways for getting POSI items?

It seems that some items are cheaper to obtain in Bazaar Sidestreets (e.g. Collated Research), while others are cheaper to make through inventory conversions (e.g. Bazaar Permists). Is there a complete list of the best sources for each high end item?

PS Also, which story rewards compete with others. (You can have only 1 ship, 1 wife, and 1 club, but what about God’s Editors, Case of Books, etc?)

The best way to get collated research is probably getting memories of distant shores from polythreme and converting them
I think i have like forty research from Polythreme and that’s just some leftovers

If you plan on making a Zubmarine then Wilmot’s End is your best friend. Whirring Contraptions are best acquired there. I used the Backstreets for Strong Backed Labour for my Zubmarine, but I had a lot of Stolen Correspondence stockpiled from the Empress’ Court to make that worthwhile. You’ll be needing a lot of Strong Backed Labour for stuff, even if you aren’t going for a Zubmarine.
edited by Sara Hysaro on 12/5/2012

There’s a list of quite a few ways to get components at [color=#00ff00]http://echobazaar.wikidot.com/components[/color] (bottom of the page) - In addition, you can get bribes from the Fidgeting Writer + stuff from one-off stories.

Regarding the second part of your question - the only unique rewards are the three you listed (Constant Companion, Club, and Ship). In all other cases, you can own multiple types of items, though (as with clothing) you can only equip one at a time.

You can also see this visually in your Expanded Inventory - note that the three unique slots are each on a line by themselves, while the three other items have empty slots to the right that can hold additional items.

Thank you for your answers.

About wiki, that reminds me of another question: there are two wikis, so is one of them more up to date, or are they both maintained equally carefully?

The wikia site seems to be updated more frequently, and personally I find that site more useful if I need to answer a specific question, like how to get a particular quality or whether a certain storylet has a rare success.

That said, the wikidot site seems more guide-oriented, and some pages on there are much more useful than their wikia counterparts: item conversions, end-game grinding, tips for zailing. The wikia site appears primarily focused on the details of individual opportunities and storylets, while the wikidot site seems more interested in higher-level strategy and analysis.