The trend worldwide is to use fewer initial capital letters in headlines and book titles than previously. Within a web site or document, be consistent.
Maximum capitalization means capitalizing all words except small unimportant words like 'of'. The title seems more serious with maximum capitalization.
Example: 'The Bestselling Guide to English Usage'
Minimum capitalization gives initial capitals only to words that normally have them, such as the first word and names of people and places. This gives a more relaxed impression.
Example: 'The bestselling guide to English usage'
Both are correct, so which to use? Follow your style guide and be consistent.