Popular with Americans.

Let's Go has shit maps and focuses primarily on what their editors deem to be the 'best' places to visit. This can be good if you are working to a limited timeframe, or you perhaps like to minimise on tough decision making.

Note that 'Nightlife' suggestions by Let's Go are well informed, and usually spot on.
This can be a real drawback with some of the other guides.
What looks good on paper does not follow to be 'good' in practice. Let's Go's emotionally loaded narrative sums up venues in a way which is funny, entertaining and saves you wasting your hard earned in bars you wouldn't visit or normally wish to visit.

Again, good if your itinary is limited.. Go for it...

Grown-up guides, perhaps more frank and witty than Lonely Planet.

Emerging roughly at the same time, Rough Guides were launched with a TV series hosted by Magenta Divine on Channel 4.

Currently with a series on Channel 5, Rough Guides have been successfully bringing their own brand of travel to the masses, something Lonely Planet struggled to achieve, despite better resources, more focused product and a loyal customer base.

All credit to Rough Guides, they have rushed in where Lonely Planet has feared to tread and if you're choosing between the two guides Rough Guides have a 'Top 50' places to visit inside the cover complete with coloured pictures, highlight and description. You can plan quickly and easily without continuously fingering the whole book.

 

Fodor's.

The French swear by them.

Personally never read one from cover to cover.
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Travel Guide book.