I have long used Lonely Planet guides, but the recent USA guides were spotty in coverage and some of the reviews of Iceland and Ireland (our destinations) were not great. Rough Guides were recommended, so I took a chance. Reviews said they were soaking with details and almost too much information. While I like too much information, I found that it was scatter shot in its unevenness. Perhaps I am comparing it to Lonely Planet, and my head thinks in a Lonely Planet way, but I could not picture my trip to either Iceland (where I've been) or Ireland (which is new). I'm someone who needs to have an idea of what to expect before I go, and Rough Guide did not do that for me.
For the most part, I'm interested in the sites and not lodging or pubs or whatever. I also like a city laid out, and Lonely Planet guides do a good job with an overview before breaking each region down. I also appreciate the Lonely Planet sidebars on saving money by buying this or that pass, or local traditions and the like. Again, I may think in a Lonely Planet way.
I can picture these guides being very useful, and taking a ton of notes as I go. For everyone who is just winging it (roughing it!) the scatter shot presentation might work great. Having not been to Ireland before, I'm not confident enough to throw my lot in with Rough Guides. Having been to Iceland, this guide just confused me and left me less confident about going back.