It partly depends on author familiarity and the reputation of the work. If a given work had some rough edges, or certain parts I don't enjoy, I'll usually stick with it based on the two. Anything under two hundred pages is a guaranteed finish unless it's particularly not working for me.
Look to experienced authors with a wide range of works. They may have many a tome to their name; yet, they usually have some much shorter works that capture part of what they are, and what they are all about. Examples:
Gore Vidal: A Search for the King, Messiah
Issac Asimov: The acclaimed Foundation series, other earlier fictional novels.
L. Niel Smith: Wardove
Thomas Pynchon: The Crying of Lot 49, Inherent Vice
Graham Greene: Pretty much any of his novels.
Charles Bukowski: Ditto.
W. Somerset Maugham: Cakes and Ale
Frederick Prokosch: The Idols Of The Cave
With all else equal, choose works written later in an author's career. This increases the chance it will be worth the struggle. Furthermore, look to authors who double as poets. Their poetry may not be well lauded, but the experience gained as poets will be noticeable in their prose. They are given to delivering greater compression, with a stronger impression; they simply make better use of your time. Frederick Prokosh and Charles Bukowski are good examples of this, despite being about as far apart in kind, and in style as you can get.
Finally, there's always the long haul. Ignore chapters. Stop where you stop and apply a bookmark. Carry on from there the next day. That's how I recently tackled Pynchon's Against the Day, and Tolkien's The Lord of the Rings (many, many, many) years ago. It works.