I don't like the middle two at all, personally.
UnitedBookstore is a nice name potentially if there are no trademark issues. In eastern Canada there is a company (which has closed some of its outlets) called United Bookstore Ltd but they seem to no have web presence under that name. I would think the name is worth lowish $$$$. On NameBio domains starting with word 'united' have sold 230 times with an average price of $1661. Domains ending in bookstore have sold 44 times (surprised so low, actually with average price of $1697.
The first name is not bad, but I will let those more expert in brandable names comment as I don't really know how to value it.
Good luck with them.