The coordinating author on the upcoming Footprints Central America is a most esteemed competitor of mine, and I have nothing but respect for his work and commitment to research - I'll highly recommend it because I know he's busting his ass. He does have a spiritual/lefty streak that might annoy you, and I know he only handles Nicaragua and Panama personally - FP's Costa Rica coverage isn't my favorite, but you don't need a guidebook for CR anymore anyway, everything is online. I think their maps are annoying, too, but at least they're useful. BUT. The fact that it's in the editorial cycle now means that the current edition is out of date; I know his deadline is this month, so it'll be out by November or so.
The Lonely Planet is considered the best guide to the region, but everyone uses it, which means if you go to one of the budget hotels it recommends, it will probably be booked and overpriced. Plus, their Nicaragua info is out of date and their El Salvador info is wrong. CR, Panama, and Guatemala are excellent, however. Don't know about Honduras and Belize. It does have, bar none, the best maps - since I'm definitely a map person, that's the selling point for me.
Fodor's is also very good, but is less comprehensive and geared to more upscale travelers - for instance, their coverage of Granada (Nicaragua) and Suchitoto (El Salvador) is surprisingly good, but only list a handful of top-end hotels and restaurants. But they just don't even mention less popular destinations except for CR and Guate - for instance, the entire Nicaraguan East Coast, with the exception of a couple ports and the Corn Islands, is omitted. Most people won't notice.
Rough Guide is substandard, even their Costa Rica section is incomplete and seems cobbled together from online research. Don't know about Frommers.
EDIT: RE: Fluff vs/ "hard info" like restaurants/hotels - I think more guidebook companies are realizing that people get hotel info online, and are shrinking those sections. If you want hostels, go to any of the hostel sites; for midrange, there's TripAdvisor, for top end, Luxurylatinamerica.com. For buses in Central America, the best place to go other than the desk at your hotel is
http://thebusschedule.com/ Since guidebook companies kind of know the writing is on the wall (and by wall, I mean Internet), they're struggling to keep guidebooks relevant in a world where you can read up-to-date reviews of 500 hotels on your phone, and that often means increasing the fluff to nuts ratio.