In reply to Roberttaylor:
Butterfield is best, but not if you're after a single described route for each hill. He dopes this, but the routes are often extremely long! He also gives a mention to alternative approaches etc, to help you devise your own routes. As someone's already said, he also lists the Tops. In my copy (don;t know if it's been updated) he uses old lists, so includes several deleted tops and the occasional long-deleted "Munro" (eg Beinn an Lochain).
If you just one a single route to tick each hill then the SMC book may be a better choice, though it can sometimes suffer from a bit of a "ticker" mentality.
McNeish's book is a bit of a mish-mash. Some routes are obviously copied from elsewhere (including repeated errors), so are on the dull side (shortest route only), but others are much better than the routes given elsewhere (eg Stuchd an Lochain and Meal Buidhe, which others describe as short there-and-back routes, McNeish suggests a much better round of Loch an Daimh with a couple of Corbetts thrown in for good measure).
If you want just one book I'd go for Butterfield - it's out of print but easy to find on the likes of abe.com or Amazon.