I love Lonely Planet. I try to mix and match guides as well -- but Lonely Planet (and one or several guides from the Dumont series) is almost always part of the mix.
I found that any of the major series can be hit or miss. I preferred Rough Guides to Lonely Planet for other destinations. Insight was really good for this trip, too.
I've yet to be disappointed by Dumont -- at least the "Richtig Reisen" and "Kunstreiseführer" lines (agreed on the Dumont minis, but with those you get what you pay for anyway). With Lonely Planet it depends on who the authors are, but those for the English speaking countries are generally pretty good ... and I used to love Tom Brosnahan's LP guides for Mexico and Central America.