I would highly recommend the LP encounter guide, especially over the Frommer's "Day by Day" format. (If you look up the Frommer's Day by Day Vienna, i have a review there that explains in more detail why I didn't like the Frommer's format.)
My trip was to both Prague and Vienna, and we stayed a few days in each city. We were looking for a small guide for each city that we could carry around all day, and didn't want to get a big book about the whole country (since this was going to be a fairly limited trip.) There seemed to be only a few brands of guides that fit in this category. I ended up with the Frommer's "Day by Day" guide for Vienna, but the latest Frommers for Prague wasn't yet available, and so I got this book - the Lonely Planet for Prague. Boy, am I glad that I did, and i wished I had the Lonely Planet as well for Vienna.
The Lonely Planet guide is very well organized. The information is primarily grouped by neighborhood, so once you've finished visiting an attraction it is easy to pick up the book and see what else is nearby. But the book also describes the "top" attractions so you can prioritize your visit. The maps are easy to follow, and make the city very easy to navigate. The book also has recommended walks and itineraries -- complete with estimated times -- that are interesting. The authors are honest about which attractions are worth visiting and which ones can be skipped. The trains and trams were well explained and it was easy for us to figure out where to buy tickets.
The book does not have hotel information, but we had booked the hotel online before leaving. Frankly, when I'm wandering around a city, I don't need to be carrying hotel information with me.
The only thing i would have liked was a little more information on the tram routes and schedules, although you could kind of figure this out by looking at the "stop" information on the larger map. Apparently Prague has a web site with the tram map posted - it might be worth printing this out before you go. The book also didn't include a pronunciation guide for the few Czech words it lists in the front.
I was worried that I might have "aged out" of the Lonely Planet guides (which I think of as appealing mostly to low budget backpackers), but we were pleasantly surprised that the book contained information relevant to many types of travelers.
Overall, I would definitely recommend taking this book with you to Prague. (I am not sure what the difference is between the LP "encounter" guide and the LP "city travel" guide, but from the table of contents it looks like the "city travel" guide uses the same exact format as this one.)