How to choose a guide book for your next trip?

I usually buy more than one guide book per trip. Where one is weak another will be stronger. I look up things I am likely to want to know. For example will you rely on your guidebook for opening hours? Then look up and see if they are there. If you're going to use the internet for opening hours, then you don't care about details like that. Do you want ideas and inspiration? Are the maps readable? If you want a little history, is there history or just a list of attractions? Does flipping through the book make you want to go right now? That's a good sign.

If it's a series, you're in a bookstore with a number of books to flip through, and there's a place you know quite well that is covered in the same series, look up things you know and see if the description matches your knowledge. That will give you an idea of the quality of the series. It might not carry over to other books in the series, but there's a good chance it will.

In my opinion the best way is to search for online reviews. Personally I like Amazon. First there are the readers reviews, secondly Amazon has this section called "What Other Items Do Customers Buy After Viewing This Item?". You can get some decent impressions with these to features of amazon.

Another possibility is to go to the local Library. Here in Belgium, the library has a decent selection of travel guides. Based on how frequently the book is borrowed, you can get an indication of its quality.

The first thing I check when comparing travel guides is when an edition was last updated. I skim read the contents of cities/towns I'm visiting to see if I can catch anything particularly important that only a newer book will have. I'm mainly bothered with transportation information as far as updated information is considered: the worst thing you want is to make your itinerary based on old data and then find it's impossible now.

Somewhat counterintuitively to the above point, if I don't find anything particular different in the transportation section I buy older editions of guides. You can get these much cheaper on Amazon or second-hand bookstores and more often than note - apart from possibly changed phone numbers and price listings - most of the information is valid anyway and I save a bundle on buying the guidebooks. What I usually need is good background information about sights to see (always remains the same), locality maps (mostly remains the same, unless roads get renamed - which in some countries like India is a major pain in the butt), and even the best cafes / restaurants / hostels are typically ones that have been around for years. Don't preclude that old editions of guidebooks are useless.

More often than not, I don't buy guidebooks. I rely on Wikitravel. What I do instead is buy proper maps in cities / towns I visit. These give me much greater detail than guidebook maps and since I like exploring a place mostly on foot, this greater map resolution helps me pinpoint places of interest better and plan my day. Maps cost a fraction of the price of guidebooks, and in smaller towns you probably don't even need to pay for one - free maps handed out by the local tourism office should suffice.

If interested in food it is essential to pick as fresh a book as possible since popular restaurants often tend to get worse over time (and the guide book reference may indeed add to such a trend).

I also want a thick one with lots of facts - not a story. If I am interested in a place I can always delve deeper on the net or buy specific books about it.

Based on these criteria I found myself with the Rough Guides most of the time with the occasional Lonely Planet or Cadogan (after a quick check of my bookshelf. If possible it is good to stick to the same publisher because they format all their books in the same way. It makes it easier to start reading the new one.