I had Lonely Planet but borrowed a Rough Guide and found it much more useful and interesting. The LP is very brief about everywhere, concentrating on certain well-trodden places. Rough Guide has much more detail, allowing you to decide better where to go and to see places off the main backpacker route. For example, my favourite chill-out place of my trip was Tadlo which gets about a three sentence write-up in LP, but is well-described in RG - it's beautiful and relaxing (but get a map of the surrounding area in Pakse first, then you can explore other waterfalls by motorbike). Unlike LP, RG had a map and better guest house listings in Mueng Noi Neua (increasing touristy and firmly on the beaten track). LP also hardly covers other regions in the south of Laos, outside of Si Phan Don.

In the north of Laos, LP asserts that the tourist board is trying to promote certain routes round the country - and then proceeds to really only describe these towns. If you only have a few days in Laos (why?!) then perhaps LP is quicker and briefer to dip into, but the RG is comprehensive and fascinating. I always find I exhaust all reading in a LP book in about a week. I also nearly always find RG maps to be clearer and more accurate than LP.

As for how accurate the books are - Laos is changing so rapidly it's impossible. Towns described as having one primitive guest house will have a ton of guesthouses and more under construction - I even heard people say places had changed immeasurably since their last visit just 2 months ago. (Hence it's useful to have a book that helps you find places off the beaten LP track.) In such places finding accommodation is even easier than the book describes and in other towns I found the information to be accurate, except that often prices were cheaper than the book described.