Lonely Planet Mongolia
It’s reasonably complete and offers a lot of practical information about every part of the country. We have not tested the 2018 update against the realities of Mongolian travel, but LP editorial standards as of late are reasonably good, we feel.
Bradt guide to Mongolia
Bradt offers a bit more background than LP, but in general, these 2 guides are almost the same. The Bradt guide has a bit more personality, and you can actually read a bit about the negatives in this guide. In terms of practical information, it offers a similar lay-out, but is less strict about the company format, which the book benefits from. Since it was last updated in 2014, LP wins.
Odyssey guide to Mongolia
Reading this book feels like a little journey in itself. This books offers all the practical information LP and Bradt give, but in a story-telling fashion with the authors own experiences woven in. More than 100 colour pictures make this book a joy to look at as well. To top it off, the Odyssey guide offers far more background information than its competitors. We recommend it, but practical information is pretty outdated, though, so you will need to supplement this with other info, either online or in print.