Which travel guide to take?

This may be ironic to be posting this on Lonely Planet's forum - but I've got a choice of literally hundreds of travel guides - online or books - which is the best to take on a trip around SE Asia and South Pacific? Do I need an actual book, or is digital content on my mobile (either pdf or app) better? Do I buy LP. Rough Guides, Frommers, etc, or do I just go with the free stuff from Expedia and Tripadvisor?

I have mixed feelings about paper-based guides. If you're lucky and you get a recent edition they provide some good basic information. The problem comes when you need accurate information about very specific places. And that's the kind of information that will make the difference between hell and bliss on your holiday.

My advice: buy a few books, do some reading and then come back to the forums and ask some questions.

It depends where you want to go, for example, LP is still the only guide that does much on Solomon Islands, though with the latest one, unless you are going to Papua New Guinea, it is definitely not worth buying the book. Just download the relevant chapters.
And remember, off the beaten track in the South Pacific, there is still only very limited internet access.

Downloading the relevant chapters is best for getting a general idea of things. Generally speaking, Lonely Planet is better for budget travellers / backpackers. Frommers is geared a little more toward the older/richer crowd.

When it comes to specifics like hotels and restaurants, I've found Tripadvisor and other online resources (these forums, blogs, etc) provide the most current and accurate information. Particularly in SE Asia, anything mentioned favourably in the LP books has usually jacked up their prices, lowered their standards, and are overrun with LP readers. Not as much of an issue in the South Pacific though due to fewer travellers.

The Moon Handbooks are pretty good. David Stanley's South Pacific one covers almost everything but I don't know if it has been updated recently (no publication date in the book itself). There are also Moon publications on Asia (not by David Stanley).