Optical Kerning adjusts the spacing between adjacent characters based on their shapes and pays no mind to the kerning pairs.
Theoretically, Optical kerning will give you more consistent character spacing, because every character pair, even the most unlikely ones like zh or xw or gk, is kerned based on its character shapes. It's a matter of preference, but here are some things to consider:
Figure 5.3. Comparison of Metrics kerning (example A) and Optical kerning (example B) using Times. The amount of difference will vary from font to font.
Figure 5.4. Metrics Kerning (example A) vs. Optical Kerning (example B) when using mixed fonts.
Figure 5.5. Metrics Kerning (example A) fares better than Optical Kerning (example B) when using script faces.
Part I: Character Formats
Going with the Flow
Getting the Lead Out
Kern, Baby, Kern
Sweating the Small Stuff: Special Characters, White Space, and Glyphs
OpenType: The New Frontier in Font Technology
Part II: Paragraph Formats
Aligning Your Type
Paragraph Indents and Spacing
First Impressions: Creating Great Opening Paragraphs
Dont Fear the Hyphen
Mastering Tabs and Tables
Part III: Styles
Stylin with Paragraph and Character Styles
Part IV: Page Layout
Setting Up Your Document
Everything in Its Right Place: Using Grids
Text Wraps: The Good, the Bad, and the Ugly